Anwendung von d-Chirasil-Val bei der gas-chromatographischen Analytik von Enantiomeren

Zusammenfassung Der Anwendungsbereich der kommerziell erhältlichen chiralen stationären Phase l-Chirasil-Val wird durch die enantiomere Phase d-Chirasil-Val beträchtlich erweitert. Bei hoher Peakauflösung wird die Präzision der Bestimmung von Enantiomerenreinheiten verbessert, da einige systematische Fehler bei vertauschter Elutionsreihenfolge ausgeschlossen werden können. Unvollständige Peakauflösung infolge von Peaktailing kann verbessert werden, wenn die Hauptkomponente nach dem in geringen Anteilen vorkommenden Enantiomer eluiert wird. Die Zuordnung von Konfigurationsisomeren wird durch Vergleich der Elutionsreihenfolge auf enantiomeren Phasen erleichtert, da der Syntheseaufwand verringert wird.

---

Application of d-chirasil-val in the analysis of enantiomers by gas-chromatography

Summary The utility of the commercially available chiral stationary phase l-Chirasil-Val is extended by the enantiomeric phase d-Chirasil-Val. Given high peak resolution, the precision of the determination of the enantiomeric purity is enhanced, excluding some systematic errors by reversing the order of peak emergence. Incomplete peak resolution caused by peak tailing is improved, when the minor enantiomer is eluted before the predominant enantiomer. The assignment of configuration isomers is simplified by correlation of the peak emergence on both enantiomers of the stationary phase, thus reducing the necessary synthetic effort.

---

---

Herrn Prof. Dr. E. Stahl, Saarbrücken, zum 60. Geburtstag gewidmet     

CO<Subscript>2</Subscript> activation on single crystal based ceria and magnesia/ceria model catalysts

Novel multifunctional ceria based materials may show an improved performance in catalytic processes involving CO₂ activation and reforming of hydrocarbons. Towards a more detailed understanding of the underlying surface chemistry, we have investigated CO₂ activation on single crystal based ceria and magnesia/ceria model catalysts. All model systems are prepared starting from well-ordered and fully stoichiometric CeO₂(111) films on a Cu(111) substrate. Samples with different structure, oxidation state and compositions are generated, including CeO_2-x/Cu(111) (reduced), MgO/CeO_2-x/Cu(111) (reduced), mixed MgO-CeO₂/Cu(111) (stoichiometric), and mixed MgO-CeO_2-x/Cu(111) (reduced). The morphology of the model surfaces is characterized by means of scanning tunneling microscopy (STM), whereas the electronic structure and reactivity is probed by X-ray photoelectron spectroscopy (XPS). The experimental approach allows us to compare the reactivity of samples containing different types of Ce³⁺, Ce⁴⁺, and Mg²⁺ ions towards CO₂ at a sample temperature of 300 K. Briefly, we detect the formation of two CO₂-derived species, namely carbonate (CO₃ ^2-) and carboxylate (CO₂ ^-) groups, on the surfaces of all investigated samples after exposure to CO₂ at 300 K. In parallel to formation of the carbonate species, slow partial reoxidation of reduced CeO_2-x/Cu(111) occurs at large doses of CO₂. The reoxidation of the reduced ceria is largely suppressed on MgO-containing samples. The tendency for reoxidation of Ce³⁺ to Ce⁴⁺ by CO₂ decreases with increasing degree of intermixing between MgO and CeO_2-x. Additionally, we have studied the stability of the formed carbonate species as a function of annealing temperature.     

The proof of Tchakaloff's Theorem

We provide a simple proof of Tchakaloff's Theorem on the existence of cubature formulas of degree for Borel measures with moments up to order . The result improves known results for non-compact support, since we do not need conditions on st moments. In fact, we reduce the classical assertion of Tchakaloff's Theorem to a well-known statement going back to F. Riesz.

     

Spin Dynamics of Negatively Charged Excitons in InP/(In,Ga)P Quantum Dots in a Magnetic Field

Physics of the Solid State - The dynamics of the photoluminescence negative circular polarization of an ensemble of InP/(In,Ga)P quantum dots is studied. It was found that, the time-resolved...     

Stability conditions in families

Publications mathématiques de l'IHÉS - We develop a theory of Bridgeland stability conditions and moduli spaces of semistable objects for a family of varieties. Our approach is based...     

Access to the Bis‐benzene Cobalt(I) Sandwich Cation and its Derivatives: Synthons for a “Naked” Cobalt(I) Source?

The synthesis and structural characterization of the hitherto unknown parent Co(bz)₂⁺ (bz=benzene) complex and several of its derivatives are described. Their synthesis starts either from a CoCO₅⁺ salt, or directly from Co₂(CO)₈ and a Ag⁺ salt. Stability and solubility of these complexes was achieved by using the weakly coordinating anions (WCAs) [Al(OR^F)₄]^? and [F{Al(OR^F)₃}₂]^? {R^F=C(CF₃)₃} and the solvent ortho‐difluorobenzene (o‐DFB). The magnetic properties of Co(bz)₂⁺ were measured and compared in the condensed and gas phases. The weakly bound Co(o‐dfb)₂⁺ salts are of particular interest for the preparation of further Co^I salts, for example, the structurally characterized low‐coordinate 12 valence electron Co(P^tBu₃)₂⁺ and Co(NHC)₂⁺ salts.     

Cell culture chip using low-shear mass transport

We have developed a flow cell that allows culturing adherent cells as well as suspended cells in a stable, homogeneous, and low-shear force environment. The device features continuous medium supply and waste exchange. In this paper, a simple and fast protocol for device design, fabrication, and assembly (sealing) based on a poly(dimethylsiloxane) (PMDS)/glass slide hybrid structure is described. The cell culture system performance was monitored, and the effective shear force inside the culture well was also determined. By manipulating the device dimensions and volumetric flow rate, shear stress was controlled during experiments. Cell adhesion, growth, proliferation, and death over long-term culture periods were observed by microscopy. The growth of both endothelial and suspension cells in this device exhibited comparable characteristics to those of traditional approaches. The low-shear culture device significantly reduced shear stress encountered in microfluidic systems, allowing both adherent and suspended cells to be grown in a simple device.