Muon spin relaxation in different samples of DyAl2

Two samples of DyAl₂ were studied by longitudial μSR in the paramagnetic and ferromagnetic regime. In a region T_c±40 K the samples give different signals although X-ray analysis can not detect any impurity phase in either of them.     

Zur intramolekularen nucleophilen Addition von 2,3-Dihydrodipyrrin-1(10H)-onen

Model compound5 was prepared by acid catalyzedintramolecular nucleophilic addition of the alcohol (Z)-4. In comparison to theintermolecular addition productl-2, differences in structure and reactivity could be determined by X-ray crystal structure analysis and¹H-NMR-spectroscopic investigations. The interpretation of these differences are based on the assumption of stereoelectronic advantages in the intermolecular adductl-2. Its methoxy group was found to beperiplanar with respect to the -(NCO)-plane of the lactam unit enabeling efficient delocalization of the amide lone pair to the *-orbital of the C-OMe-bond. The orientation of the corresponding C-O-bond in5 is fixed by the rigid structure of the bicyclic ring system and can be classified assynclinal. Consequentlyl-2 eliminates methanol very easily under acidic or high temperature conditions, whereas5 is a stable compound.In the stereoelectronically favoured adductl-2 n *-delocalization increases elimination reactivity on the one hand and thermodynamic stability on the other hand. Therefore adducts of this kind may be good candidates for biological regulators—a matter of interest with regard to the protein-chromophore interaction in biliproteins.

     

Hyperbolicity of the complement of plane curves

In this paper it is proved that the complement in ₂ of a holomorphic curve D of genus g2 is a hermitian hyperbolic complex manifold provided that certain conditions on the singularities of the dual D* of D are satisfied and that every tangent at D* intersects D* in at least two distinct points.Dedicated to Karl Stein     

Synthesis and evaluation of antitrypanosomal activity of some thiosemicarbazide derivatives of 1-butyl-6-fluoro-7-morpholino-4-oxo-1,4-dihydroquinoline-3-carboxylic acid

The synthesis of thiosemicarbazide of 1-butyl-6-fluoro-7-morpholino-4-oxo-1,4-dihydroquinoline-3-carboxylic acid as well as its heterocyclic derivatives – 1,3,4-thiadiazole and 1,2,4-triazole are described; the modification of proper 1,2,4-triazole derivative by maleimides is also presented. Spectral properties of the prepared compounds and X-ray analysis for the selected compounds were studied. For the compounds antitrypanosomal potential and the toxicity were determined.     

Atomic-Scale Studies of Fe3O4(001) and TiO2(110) Surfaces Following Immersion in CO2-Acidified Water

Difficulties associated with the integration of liquids into a UHV environment make surface-science style studies of mineral dissolution particularly challenging. Recently, we developed a novel experimental setup for the UHV-compatible dosing of ultrapure liquid water and studied its interaction with TiO₂ and Fe₃O₄ surfaces. Herein, we describe a simple approach to vary the pH through the partial pressure of CO₂ ( ) in the surrounding vacuum chamber and use this to study how these surfaces react to an acidic solution. The TiO₂(110) surface is unaffected by the acidic solution, except for a small amount of carbonaceous contamination. The Fe₃O₄(001)-( × )R45° surface begins to dissolve at a pH 4.0–3.9 ( =0.8–1 bar) and, although it is significantly roughened, the atomic-scale structure of the Fe₃O₄(001) surface layer remains visible in scanning tunneling microscopy (STM) images. X-ray photoelectron spectroscopy (XPS) reveals that the surface is chemically reduced and contains a significant accumulation of bicarbonate (HCO₃⁻) species. These observations are consistent with Fe(II) being extracted by bicarbonate ions, leading to dissolved iron bicarbonate complexes (Fe(HCO₃)₂), which precipitate onto the surface when the water evaporates.     

Development of Passive and Active Barrier Coatings on the Basis of Inorganic–Organic Polymers

Summary. With a new kind of barrier coating material, namely inorganic–organic polymers, it is possible to obtain excellent barrier properties against oxygen, water vapor, and flavor permeation. These hybrid polymers can be synthesized by the sol–gel technique. If extremely low permeation values are needed, the combination of hybrid polymer coatings with thin inorganic oxidic layers (SiO_x, AlO_x) is very effective and leads to permeation values for oxygen and water vapor below 10⁻³ cm³/m² · d · bar or g/m² · d. These passive barrier layers can be further improved by the combination with active oxygen barrier layers which have been developed for the food packaging industry. This approach makes these multilayer laminates promising candidates for special applications in the food packaging industry as well as for sophisticated applications in technical areas: the encapsulation of sensitive organic devices like solar cells, organic light emitting diodes, or polymer electronic systems.     

Quantitation of talinolol and other beta-blockers by capillary electrophoresis for in vitro drug absorption studies

A capillary zone electrophoresis method is described for the enantioseparation of talinolol using heptakis(2,3-diacetyl-6-sulfo)-beta-cyclodextrin (HDAS-beta-CD) as a chiral selector. After liquid-liquid extraction of talinolol from physiological solution, electrokinetic injection was employed to improve the sensitivity. The use of a coated capillary was necessary to achieve stable and reproducible enantioseparations. A baseline separation of the talinolol enantiomers was achieved in less than 10 min using 100 mM phosphate solution as background electrolyte and pH 3.5, at the presence of 3.0 mM HDAS-beta-CD and at 20 degrees C. In addition, this analytical condition proved to be useful for the enantioseparation of a number of other beta-blocking agents such as alprenolol, atenolol, bisoprolol, celiprolol, metipranolol, oxprenolol, and sotalol. For determining talinolol, the method could be validated in terms of precision, accuracy and linearity, and was found to be suitable in determination of talinolol enantiomers in highly diluted samples obtained from in vitro experiments.     

Mechanistic study of the reactivity of 3,4-epoxycyclohexylmethyl 3′,4′-epoxycyclohexancarboxylate in photoinitiated cationic polymerizations

An investigation of the reactivity of the cycloaliphatic diepoxide, 3,4-epoxycyclohexyl 3′, 4′-epoxycycloexane carboxylate ( I ) in photoinitiated cationic polymerization was carried out with the aid of model compounds. It was shown that the presence of the ester group greatly retards the rate of polymerization of this bisepoxide. Molecular modeling studies indicate that the ester carbonyl group can interact in a number of ways with the initially formed protonated or alkylated oxiranium cation to give bicylic dialkoxycarbenium ions. These latter species are both more sterically hindered and less reactive than the oxiranium cation precursors and undergo propagation at a considerably reduced rate. Reactivity studies em-ploying model compounds also showed that epoxy monomers that contain ester groups undergo polymerization at much slower rates than those in which the ester group is absent. © 1995 John Wiley & Sons, Inc.     

The synthesis and study of the photoinitiated cationic polymerization of novel cycloaliphatic epoxides

The synthesis of a series of difunctional epoxides bearing two epoxycyclohexyl groups linked together by an alkylene ether group has been carried out. Subsequently, the reactivities of these novel monomers was investigated and compared to the reactivity of the cycloali-phatic epoxide, 3,4-epoxycyclohexylmethyl 3′,4′-epoxycyclohexane carboxylate ( I ) in pho-toinitiated cationic polymerization. It was observed that alkylene oxide linking the two epoxycyclohexyl groups was short and the monomers are more reactive than I . The effects of the photoinitiator structure and the experimental conditions of the cationic photopo-lymerization on the rates was also studied using real-time infrared spectroscopy. © 1995 John Wiley & Sons, Inc.     

Optical investigations of alkali metal thiomanganates(II) containing isolated complexes as well as chain and planar compounds

Tetracoordinated Mn(II) complexes providing different molecular structures were investigated using various spectroscopical procedures. Na(6)MnS(4) contains separate pseudotetrahedral Mn-S complex units, K(2)MnS(2) has chains of edge-shared tetrahedra, and Cs(2)Mn(3)S(4) crystallizes in corresponding layers. Also doped materials, i.e., Cs(2)(Mn(x)Zn(1-x))(3)S(4) with 0.0 < x < 1.0, are considered. Absorption spectra recorded from samples incorporated in polyethylene pellets and excitation spectra taken from pure materials at 15-20 K temperature are assigned on the basis of energy level calculations obtained from the angular overlap model. All compounds exhibit intensive emission in the red, some of them also in the yellow region, which both are investigated in the temperature range from 12.5 to 250 K, in some cases varying the excitation power and excitation wavelength. Decay measurements supply lifetimes and activation energies evaluated from Arrhenius plots. The results support an assignment of both types of emissions to MnS(4) complex entities for all compounds, the red emission from the lowest excited level (Kasha luminescence) and the yellow emission, observed for some of the compounds with increasing intensity at lower temperature, from higher electronic levels.