Molecular Ln(III)−H−E(II) Linkages (Ln=Y,Lu; E=Ge,Sn, Pb)

Following the alkane-elimination route, the reaction between tetravalent aryl tintrihydride Ar*SnH₃ and trivalent rare-earth-metallocene alkyls [Cp*₂Ln(CH{SiMe₃}₂)] gave complexes [Cp*₂Ln(μ-H)₂SnAr*] implementing a low-valent tin hydride (Ln=Y, Lu; Ar*=2,6-Trip₂C₆H₃, Trip=2,4,6-triisopropylphenyl). The homologous complexes of germanium and lead, [Cp*₂Ln(μ-H)₂EAr*] (E = Ge, Pb), were accessed via addition of low-valent [(Ar*EH)₂] to the rare-earth-metal hydrides [(Cp*₂LnH)₂]. The lead compounds [Cp*₂Ln(μ-H)₂PbAr*] exhibit H/D exchange in reactions with deuterated solvents or dihydrogen.     

Tetryl-Tetrylene Addition to Phenylacetylene

Phenylacetylene adds [Ar*GeH₂-SnAr’], [Ar*GeH₂-PbAr’] and [Ar'SnH₂-PbAr*] at rt in a regioselective and stereoselective reaction. The highest reactivity was found for the stannylene, which reacts immediately upon addition of one equivalent of alkyne. However, the plumbylenes exhibit addition to the alkyne only in reaction with an excess of phenylacetylene. The product of the germylplumbylene addition reacts with a second equivalent of alkyne and the product of a CH-activation, a dimeric lead acetylide, were isolated. In the case of the stannylplumbylene the trans-addition product was characterized as the kinetically controlled product which isomerizes at rt to yield the cis-addition product, which is stabilized by an intramolecular Sn–H–Pb interaction. NMR chemical shifts of the olefins were investigated using two- and four-component relativistic DFT calculations, as spin–orbit effects can be large. Hydride abstraction was carried out by treating [Ar'SnPhC=CHGeH₂Ar*] with the trityl salt [Ph₃C][Al(OC{CF₃})₄] to yield a four membered ring cation.     

Structure of synthetic transmembrane lipid membranes at the solid/liquid interface studied by specular X-ray reflectivity

We fabricated a new class of supported membranes based on monolayers of artificial bola (transmembrane) lipids. The lipids used in this study are symmetric bola lipids with two phosphocholine head groups, which resemble natural archaea lipids. To prevent bending of the hydrocarbon chains, stiff triple bonds are inserted in the middle of the hydrocarbon cores. The formation of homogeneous "monolayers" of transmembrane lipids over macroscopic areas can be monitored with fluorescence microscopy. Structures of such supported monolayers in bulk water were characterized with specular X-ray reflectivity using high energy X-ray radiation, which guarantees a high transmission through bulk water. Here, the vertical structure of single monolayers could be resolved from reconstructed electron density profiles. To verify the structural model suggested by the specular reflectivity, we also performed small- and wide-angle X-ray scattering of transmembrane lipid suspensions. The wide-angle patterns reflect a distorted chain-chain correlation, while the small-angle scattering allowed us to model an electron density profile which is consistent with the profile calculated from specular reflectivity.     

Unraveling the metabolic transformation of tetrazepam to diazepam with mass spectrometric methods

The metabolic transformation pathways of the 1,4-benzodiazepine tetrazepam (C(16)H(17)ClN(2)O, average mass: 288.772) were studied with capillary LC-QqTOF-MS and -MS/MS by analyzing human plasma and urine samples collected from healthy volunteers. Each volunteer took 50 mg of tetrazepam, given in the form of one tablet of Myolastan (Sanofi-Synthelabo, Vienna, Austria). Accurate molecular mass measurements in full-scan mode (scan range: 50-700) were used to survey the collected samples for putative metabolic transformation products. Full-scan fragment ion mass spectra were collected in subsequent LC/MS/MS experiments. Each spectrum was matched to a spectral library containing 3759 MS/MS-spectra of 402 compounds, including eighteen different benzodiazepines, to prove the structural relatedness of a tentative metabolite to tetrazepam. This "similarity search" approach provided a rapid and powerful tool to exclude non-drug-related species, even without any knowledge of the fragmentation chemistry. Interpretation of tandem mass spectrometric data was only required in order to elucidate the site of transformation. Using this strategy, 11 major classes of tetrazepam metabolites were identified. Possible metabolic routes from tetrazepam to diazepam (C(16)H(13)ClN(2)O, average mass: 284.740) via repeated hydroxylation and dehydration of the cylohexenyl moiety were discovered. No evidence for extensive hydroxylation of tetrazepam at position 3 of the diazepine ring was found. In contrast to what is commonly believed, this distinct transformation reaction may be of only minor importance. Furthermore, the occurrence of demethylation, hydration, and glucuronidation reactions was proven.     

Persulfonylation of amines applied to the synthesis of higher generation dendrimers

Systematic analysis of the persulfonylation of branched aromatic oligoamines with different arylsulfonyl chlorides allowed optimization of the repetitive steps involved in the synthesis of the sulfonimide-based dendrimers. The optimized procedures afforded the fourth generation N- and pentaphenylene-centered dendrimers with 16 and 32 peripheral groups, respectively. Analysis of products of incomplete substitution showed that the amino groups in aromatic oligoamines are persulfonylated consecutively.     

Surface Modification and Functionalization of Metal and Metal Oxide Nanoparticles by Organic Ligands

Summary. Metal or metal oxide nanoparticles possess unique features compared to equivalent larger-scale materials. For applications, it is often necessary to stabilize or functionalize such nanoparticles. Thus, modification of the surface of nanoparticles is an important chemical challenge. In this survey, various possibilities are discussed how nanoparticles can be protected by organic ligands and how these ligands can be used to introduce functionalities. The preparative possibilities include grafting of an already functionalized ligand on the nanoparticle surface, exchanging part or all existing ligands on the nanoparticle surface, or grafting of a ligand on a nanoparticle followed by modification by organic chemical reactions.     

Magnetically-coupled piston pump for high-purity gas applications

Experiments based on noble elements such as gaseous or liquid argon or xenon utilize the ionization and scintillation properties of the target materials to detect radiation-induced recoils. A requirement for high light and charge yields is to reduce electronegative impurities well below the ppb (parts per billion, 1 ppb \(=1\times 10^{-9}\) mol/mol) level. To achieve this, the target material is continuously circulated in the gas phase through a purifier and returned to the detector. Additionally, the low backgrounds necessary dictate low-Rn-emanation rates from all components that contact the gas. Since commercial pumps often introduce electronegative impurities from lubricants on internal components or through small air leaks, and are not designed to meet the radiopurity requirements, custom-built pumps are an advantageous alternative. A new pump has been developed in Muenster in cooperation with the nEXO group at Stanford University and the nEXO/XENON group at Rensselaer Polytechnic Institute based on a magnetically-coupled piston in a hermetically sealed low-Rn-emanating vessel. This pump delivers high performance for noble gases, reaching more than 210 standard liters per minute (slpm) with argon and more than 170 slpm with xenon while maintaining a compression of up to 1.9 bar, demonstrating its capability for noble gas detectors and other applications requiring high standards of gas purity.     

MALDI‐TOF MS Coupled with Collision‐Induced Dissociation (CID) Measurements of Poly(methyl methacrylate)

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) was chosen for an in‐detail analysis of poly(methyl methacrylate) (PMMA) in order to determine the possible fragmentation mechanism with the help of collision‐induced dissociation (CID). All experiments were performed on a well‐defined PMMA standard and were optimized for sample preparation and measurement conditions of both MS and MS/MS. In order to investigate the fragmentation pathways, two parent peaks—both charged with sodium (m/z = 1 625.9 and 2 226.2 Da, respectively)—were selected, thus permitting the examination of possible cleavages, and reaction pathways. For both chosen peaks, the MALDI‐TOF MS/MS spectra revealed four fragmentation series that could be explained by single or multiple main chain scissions and secondary reactions of the PMMA side groups. According to the molar mass of the fragments, a loss or migration of the side group to the end of the free radical, followed by a β‐scission, was favored. These insights are the first steps toward the construction of a library with fragments and fragmentation pathways, complementary to proteomics libraries, in order to obtain fast and automated identification of substances.

     

Hydrothermal convection in moderately thin spherical shells

Hydrothermal convection of pore water with a temperature-dependent viscosity within a permeable, internally heated, moderately thin spherical shell is investigated by both a perturbation analysis and a direct numerical simulation. The analysis and simulation are mainly focused on a thin spherical shell in that convective instabilities are characterized by the spherical harmonic degree l=6 with a 13-fold mathematical degeneracy. Four different three-dimensional analytical solutions of convection are derived by removing the degeneracy through the nonlinear effect. A direct numerical simulation of the nonlinear problem is also carried out, showing satisfactory agreement between the analytical solutions and the numerical simulations.     

Surface Chemistry of Planarized SiLK-Films Studied by XPS

 SiLK^** is an isotropic, low dielectric constant polymer specifically designed as new passivation layer within the existing Al/W based metallizations schemes in microelectronic applications. The deposition of the polymer on Al patterned lines causes a topography, which must be afterwards planarized by a chemical-mechanical polishing process (CMP). The changes in the surface chemistry of SiLK^** as result of this process using commercially available slurries were investigated by X-ray photoelectron spectroscopy (XPS) taking into account C 1s/O 1s core levels, shake up effects and SiLK valence bands. Oxidized carbon species were found on top of the polymer surface as a residue of the CMP. There concentrations containing at least hydroxyl reactive groups show a dependence on the slurry pH-value. The concentration increases at acid degrees far from the neutral point, the minimum position.