Treatment of citrate-capped Au colloids with NaCl, NaBr and Na2SO4: a TEM, EAS and EPR study of the accompanying changes

In the present study, effects of the treatment of citrate-reduced Au sols with NaCl, NaBr and Na₂SO₄ are described. The particles are characterized by transmission electron microscopy (TEM) and spectroscopic methods, suggesting an exchange of the citrate capping by the anions of the Na salts. Under electron beam exposure the capping of the NaCl- and NaBr-treated particles disappears. The specific electronic properties of the Na salt-treated particles are studied by electron absorption spectroscopy (EAS) and electron paramagnetic resonance (EPR). A discussion of the results in comparison with the spectroscopic responses from the original particles is given. A correlation between the data of EAS and EPR is found. The respective electron-withdrawing effect of the capping anions towards the Au core seems to be of considerable significance regarding the orbital situation around the Fermi level.     

Reaktionen von aminofluorosilanen zu vier- bis siebengliedrigen ringsystemen

The reaction of N,N′-dimethylurea, N,N′-dimethylethylenediamine and t-butylamine with fluorosilyl-substituted disilazanes leads after primary lithiation with butyllithium to the formation of the six, seven- and four-membered rings I–III. The five- and seven-membered rings IV and V were prepared in a comparable reaction with the disodium salt of ethyleneglycol.     

Enantioselective BINOL-phosphoric acid catalyzed Pictet-Spengler reactions of N-benzyltryptamine

Optically active tetrahydro-beta-carbolines were synthesized via an ( R)-BINOL-phosphoric acid-catalyzed asymmetric Pictet-Spengler reaction of N-benzyltryptamine with a series of aromatic and aliphatic aldehydes. The tetrahydro-beta-carbolines were obtained in yields ranging from 77% to 97% and with ee values up to 87%. The triphenylsilyl-substituted BINOL-phosphoric acid proved to be the catalyst of choice for the reaction with aromatic aldehydes. For the aliphatic aldehydes, 3,5-bistrifluoromethylphenyl-substituted BINOL-phosphoric acid was identified as the best catalyst.     

Asymmetric alkylation of N‐acylisoindolin‐1‐ones via α‐bromoimides: A novel route to 1‐substituted isoindolines

Key intermediate in the synthesis of the title compounds 9a‐c and 10a‐c was the chiral α‐bromoimide 1 which has been prepared by radical bromination of the corresponding N‐acylisoindolin‐1‐one 13. 1 was alkylated with silyl enol ethers under Lewis acid catalysis using α‐amidoalkylation methodology. N,N‐diacyliminium ion 14 is presumably the intermediate in this reaction. Further transformations of the alkylated compounds yielded 1‐substituted isoindolines as target compounds.     

First-principles statistical mechanics study of the stability of a subnanometer thin surface oxide in reactive environments: CO oxidation at Pd(100)

We employ a multiscale modeling approach to study the surface structure and composition of a Pd(100) model catalyst in reactive environments. Under gas phase conditions representative of technological CO oxidation (approximately 1 atm, 300-600 K) we find the system on the verge of either stabilizing subnanometer thin oxide structures or CO adlayers at the surface. Under steady-state operation this suggests the presence or continuous formation and reduction of oxidic patches at the surface, which could be key to understand the observable catalytic function.     

Silver as acrolein hydrogenation catalyst: intricate effects of catalyst nature and reactant partial pressures

The hydrogenation of acrolein over pure and supported silver has been investigated with a focus on the influence of catalyst structure and reaction pressure (mbar to 20 bar range) on activity and selectivity. An onset of formation of allyl alcohol beyond 100 mbar reaction pressure (at 250 degrees C) is ascribed to a change in adsorption geometry upon increasing coverage. Smaller silver particles (in the nanometer range), the proximity of a reducible oxide component as well as high pressure lead to enhanced allyl alcohol formation; the selectivity to the other main product propionaldehyde is reduced. The silver dispersion changed depending on the reaction pressure. Moreover, the presence of oxygen, most likely as subsurface oxygen, and the presence of defects are of paramount importance for the catalytic behaviour. The considerable changes of the silver catalysts under reaction conditions and the pressure dependence call for in situ measurements to establish true structure-activity/selectivity relationships for this system.     

Szentiamide, an N-formylated cyclic depsipeptide from Xenorhabdus szentirmaii DSM 16338T

Szentiamide (1) a new cyclic hexadepsipeptide was isolated from the culture broth of the entomopathogenic bacterium Xenorhabdus szentirmaii DSM 16338T. The structure was elucidated by analysis of one- and two-dimensional NMR spectra and high resolution mass spectrometry. The amino acids were determined to be D-leucine, L-threonine, D-phenylalanine, D-valine, L-tyrosine and L-tryptophane after hydrolysis and derivatization with D-FDVA [Nalpha-(2,4-dinitro-5-fluorophenyl)-D-valinamide].     

Photostability of sunscreens

Sunscreens were originally designed to include mainly UVB-filters. Because of the deeper penetration of UVA light, causing photoaging and DNA damage, there has been a shift towards broad spectrum sunscreens. These broad spectrum sunscreens now include both UVA- and UVB-filters and other ingredients which possess antioxidant activity. Although sunscreens are regulated in most countries, photostability testing is not mandatory. Because of the ability of sunscreen ingredients to absorb UV-light and the complexity of most of these formulations, which may include more than one UV-filter, antioxidants and other formulation excipients, it is important that their photostability in combination is determined.     

Benzoylphosphonate-Based Photoactive Phosphopeptide Mimetics for Modulation of Protein Tyrosine Phosphatases and Highly Specific Labeling of SH2 Domains

A light switch for phosphotyrosine- recognizing proteins: Irradiation of the bioisosteric benzoylphosphonate suffices to "turn off" the activity of target proteins and to label them covalently. Photoactive bioisosters may find applications in functional cell biology, bioanalytics, and proteome research.