Asymptotics at infinity of solutions to the Neumann problem in a sieve-type layerComportement asymptotique à l'infini d'un problème de Neumann dans une couche perforée

The Neumann problem is considered in a domain $\text{Ω}$, which can differ from a periodic layer inside a compact set. We prove the Fredholm property of the corresponding operator in step-weighted Sobolev spaces and determine its kernel and cokernel. All these results are based on the obtained asymptotic representation of solutions at infinity. To cite this article: S.A. Nazarov, G. Thäter, C. R. Mecanique 331 (2003).     

Die Fundamentalsätze der Flächentheorie in einem affinen Raum mit Areal

Ohne ZusammenfassungDiese Arbeit wurde von der Deutschen Forschungsgemeinschaft im Rahmen einer Sachbeihilfe gefördert, wofür wir auch an dieser Stelle unseren Dank aussprechen möchten.     

Zur reaktion von tricyclopentadienyl-lanthanoid-komplexen mit 1-alkinen

Contrary to the prediction based on published pK₃-data (for cyclopentadiene and phenylethyne), Cp₃Ln^III-complexes react readily with various 1-alkynes, HCCR, by liberating cyclopentadiene. While for Ln = Yb and R = n-alkyl the formation of the novel metallacycles [Cp₂YbCCR]₃ involving

bridges and quite exceptional ¹H NMR spectroscopic features is preferred, the “lighter” Ln-element Nd apparently avoids the formation of corresponding {Cp₂NdCCR} moieties with still intact μ-(CCR) ligands in favour of a partial regeneration of Cp₃Nd.     

Use of reporter cell lines for detection of endocrine-disrupter activity

We have studied stable transformed human mammary cell lines with highly inducible steroid receptor-mediated luciferase reporter gene expression. Cells responding specifically to glucocorticoids, progestagens, androgens, or estrogens are described and characterized. The use of this high-throughput, cell-based assay for analysis of steroid (ant)agonists is reported. Systematic characterization of endocrine-disrupting activity on human receptors and in a human-cell system is interpreted for a selection of xenobiotics. We show that the phytoestrogens apigenin and genistin have progestagenic and androgenic activity, respectively. Finally, application of cell-based assays to the analysis of environmental samples is discussed.     

Comparison of thioethers and sulfoxides as axial ligands for N-acetylmicroperoxidase-8: implications for oxidation of methionine-80 in cytochrome c

Methionine-80 (Met-80) in mitochondrial cytochrome c (cyt c) can be oxidized to the corresponding sulfoxide by reactive oxygen species, a reaction of potential biological significance. As an approach to investigating how oxidation of Met-80 would influence its interactions with heme iron, we have examined binding of 2-(methylthio)ethanol (MTE) and dimethyl sulfoxide (DMSO), models for the side chains of Met and Met(SO), respectively, to ferrous and ferric N-acetylmicroperoxidase-8 (AcMP8). We find that DMSO coordinates 1.2 kcal/mol less strongly to Fe(III)-AcMP8 than does MTE, although both ligands form low-spin complexes. Comparison of spectroscopic data for the DMSO complex of Fe(III)-AcMP8 with published data for the Met(SO)-80 form of ferric cyt c allows us to conclude that Met(SO)-80 does not coordinate to iron in the latter. DMSO coordinates to Fe(II)-AcMP8 1.3 kcal/mol more strongly than does MTE, whereas Met-80 and Met(SO)-80 are reported to have approximately equal affinity for Fe(II) in cyt c. This result suggests that the steric environment near the heme iron in cyt c discriminates against coordination of Met(SO)-80. Vacuum quantum chemical density functional theory calculations confirm the greater affinity of the sulfoxide and show that coordination via oxygen is strongly favored. Resonance Raman spectroscopic data indicate that the preference for coordination via oxygen is maintained in solution. The computational data further indicate that the DMSO complex derives significant enthalpic stabilization from pi back-bonding but that iron to sulfur pi back-bonding does not make a significant contribution to bonding in the thioether complex.     

Hydrogen storage capacity of catalytically grown carbon nanofibers

In 1996, R. T. K. Baker, and N. M. Rodriguez claimed to have synthesized a new type of carbon nanofiber material capable of storing large amounts of hydrogen at room temperature and pressures above 100 bar, thus making it a powerful candidate for a very efficient energy storage system in mobile applications. Consequently, many scientists all over the world tried to test and verify these findings, however, with partly inconsistent results. We present here for the first time independent hydrogen storage measurements for several types of nanofibers, both synthesized by our group following precisely the specifications given in the literature as well as original samples supplied by Rodriguez and Baker for this study. The hydrogen storage capacities at room temperature and pressures up to 140 bar were quantified independently by gravimetric and volumetric methods, respectively. No significant hydrogen storage capacity has been detected for all carbon nanofibers investigated.     

The excited-state chemistry of phycocyanobilin: a semiempirical study.

Based on previous time-resolved absorption studies, phycocyanobilin undergoes a photoreaction from an A- into a B- and C-form, with the latter two photoproducts showing absorption spectra red-shifted from A. To identify the molecular mechanism involved in the excited-state reactions, the structural origin of the red shift in the absorption spectra is investigated. Using semiempirical AM1 calculations that include configuration interaction by pair doubles excitation configuration interaction, the absorption spectra of different conformers as well as different protonation states were calculated. The results clearly indicate a pronounced red shift in the spectra of structures either protonated or deprotonated at the basic/acidic centres of the tetrapyrrole chromophore whereas, in contrast, conformational changes alone result in a blue shift. Furthermore, it is shown by quantum chemical calculations that the basicity of phycocyanobilin is much higher in the excited than in the ground state, with a decrease in the excited-state pK(B)* of approximately 9.5 units. The acidity is only slightly enhanced with a drop in pK(A)* of only approximately 1.6 units. From these findings, a reaction model for the excited-state processes in phycocyanobilin is proposed. According to this model, photoexcitation of phycocyanobilin triggers an excited-state proton transfer giving rise to the formation of a protonated species. In parallel, the local increase in the medium pH associated with protonation then forwards a deprotonation at an acidic NH-group so that in effect both protonated and deprotonated phycocyanobilin would arise from the initial photoreaction and account for the observed red shift in the spectra of the B- and C-forms.     

In Situ Induction of Strain in Iron Phosphide (FeP2) Catalyst for Enhanced Hydroxide Adsorption and Water Oxidation

Carbon‐based materials have been widely used in heterogeneous catalysis because of their advantages of high surface area, thermal stability, and chemical inertness. However, their role in the catalysis is not fully understood although most studies conclude that the coupling between the carbon support and catalyst could reduce the charge transfer resistance and improve the kinetics of catalytic reactions such as water splitting. In this study, a carbon‐modified FeP₂ electrocatalyst with a one‐step strategy is synthesized. The tensile strain is introduced in situ in the ab crystal plane of the FeP₂ catalyst. This leads to charge redistribution between H and O atoms in the OH bonds and enhances the adsorption of reaction intermediates. In the water oxidation process, this results in a decrease in the energy barrier for the rate‐determining step, specifically, the chemical step of *OH adsorption preceded by one‐electron transfer. Benefiting from the optimized adsorption energy, the strained catalysts exhibit excellent oxygen evolution reaction (OER) activity with a low overpotential in addition to their increased stability. This study provides a new strategy for the introducing of strains in functional materials and provides new insights into the influence of carbon modification on OER activity.     

Tunable porosity in bridged organosilicas using self-organizing precursors

Functionalized, mesoporous organosilicas with tunable porosity were prepared by a direct and simple approach from rationally designed precursors, combining the function of a network builder and a porogen in one molecule. The precursors are synthesized using a dual hydroboration reaction, fulfilling the criteria of "click-chemistry", first on an ethylene-bridged organosilica and then on a long-chain alkene. Thus, in the final molecule the boron atom connects the sol-gel precursor (the bridged organosilica) with the porogen (the long-chain alkene). The so-prepared precursors do self-organize when hydrolysis of their inorganic moiety takes place via an aggregation of their organic side chains into hydrophobic domains. The length of the attached chain influences the size of the hydrophobic domain and thus, after a condensation-aminolysis sequence, the finally observed porosity of the organosilicas. Depending on chain length micro- to mesoporous materials with average pore sizes from 1.5 to 4.1 nm (for attached pentene to hexadecene chains) are observed. Furthermore, the boron entity enables the subsequent introduction of various functional groups into the pore walls of the organosilica networks. Amine or hydroxyl functionalities can be easily introduced, dependent on the experimental conditions used during the borane cleavage and extraction step. The accessibility of these functionalities can be proven by a significant metal adsorption onto the functional organosilica walls.