Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Synthesis of functionalized 2-alkylidenetetrahydrofurans by cyclization of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with epoxides

The Lewis acid mediated cyclization of epoxides with 1,3-bis(trimethylsilyloxy)-1,3-butadienes, electroneutral equivalents of 1,3-dicarbonyl dianions, results in the formation of 2-alkylidenetetrahydrofurans with a great variety of substitution patterns and functional groups. This includes the synthesis of 2,3'-bifuranylidenes and 7-oxabicyclo[4.3.0]nonanes. The cyclization of dienes with functionalized epoxides containing base-labile groups proceeds with good chemoselectivity. In all reactions, good regio- and E diastereoselectivities are observed. Based on the stereoselectivities observed for reactions of 1,2-disubstituted epoxides, a working hypothesis for the mechanism of the reaction is suggested.     

Dipolar control of monolayer morphology: spontaneous SAM patterning

A strategy for controlling relative placements of molecules within multicomponent monolayers at the solution-HOPG interface is demonstrated. The monolayers assemble from complementary pairs of 1,5-bis-alkyldiether-anthracenes bearing self-repelling side chains. Each diether side chain suffers repulsive dipolar interactions if it adsorbs next to an identical side chain in the morphology normally assumed by 1,5-bis-substituted-anthracene monolayers. Complementary side-chain pairs experience attractive dipolar interactions when adsorbed as neighbors in the normal morphology monolayer. The repulsive and attractive forces spontaneously drive formation of a patterned monolayer at the solution-HOPG interface. Each molecule adsorbs in its own row, sandwiched between two rows of the complementary anthracene. These studies demonstrate the viability of using weak dipolar interactions to control molecular placement and monolayer morphology and to pattern multicomponent monolayers.     

Adsorption dynamics of ethylene on Si(001)

The dynamics of ethylene adsorption on the Si(001) surface was investigated by means of molecular beam techniques. A constant decrease of initial sticking probability s(0) was observed with increasing kinetic energy indicating a non-activated adsorption channel. With increasing surface temperature, s(0) decreases as well, pointing towards adsorption via a precursor state. Quantitative evaluation of the temperature dependence of s(0) via the Kisliuk model was possible for surface temperatures above 250 K; below that value, the temperature dependence is dominated by the adsorption dynamics into the precursor state. Maximum surface coverage was found to be reduced with increasing surface temperature, which is discussed on the basis of a long lifetime of the precursor state at low temperatures.     

Intercalation of Toluidines into α-Zirconium Hydrogenphosphate

Intercalates of o-, m-, and p-toluidine into α-Zr(HPO₄)₂ · H₂O were prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. As follows from IR, toludine molecules are protonated in the interlayer space. Toluidine molecules are arranged in a bimolecular way in the intercalates containing more than 1.5 toluidine molecules per Zr atom. On the other hand, a monolayer of the toluidine molecules is supposed in the intercalates with less than one toluidine molecule per Zr atom.     

Time-resolved two-photon photoemission of unoccupied electronic states of periodically rippled graphene on Ru(0001)

The unoccupied electronic states of epitaxially grown graphene on Ru(0001) have been explored by time- and angle-resolved two-photon photoemission. We identify a Ru derived resonance and a Ru/graphene interface state at 0.91 and 2.58?eV above the Fermi level, as well as three image-potential derived states close to the vacuum level. The most strongly bound, short-lived, and least dispersing image-potential state is suggested to have some quantum-well character with a large amplitude below the graphene hills. The two other image-potential states are attributed to a series of slightly decoupled states. Their lifetimes and dispersions are indicative of electrons moving almost freely above the valley areas of the moiré superstructure of graphene.