Derivate der 5,6-Dihydro-2H-pyran-3-carbonsäure

Summary Some derivatives of 5,6-dihydro-2H-pyran-3-carboxaldehyde (7) and of its oxidation product 5,6-dihydro-2H-pyran-3-carboxylic acid (8) have been prepared. The aldehyde derivatives as well as the amides and esters of8 have been tested in an insecticidal/fungicidal/acaricidal screening programme. The methylester35 shows a distinct knock down effect against the fruit flyDrosophila melanogaster.

     

Thin-layer chromatography and multivariate data analysis of willow bark extracts

In most cases the pharmacological activity of plant extracts is not assigned to single components and often not all active ingredients are known. Approaches other than those considering single compounds only to analyze plant material have proven helpful for a better characterization of extracts in their entirety. In this study extracts of willow bark are analyzed by high-performance thin-layer chromatography (HPTLC) and two different pharmacological tests [the 2,2'-azobis (2-amidinopropane) dihydrochloride reaction and the xanthine/xanthine oxidase reaction] with the help of multivariate data analysis. Described are two models using the results of the chromatographic study of 22 various extracts of willow bark and their pharmacological properties. The chromatographic data are obtained by a special TLC scanner that enables measurement of HPTLC tracks simultaneously in the range of lambda = 200-400 nm. Additionally, the developed models are used to predict the activity of another three extracts of willow bark demonstrating the quality of the model.     

Synthese und Eigenschaften einiger neuer Mono(π-cyclopentadienyl)-Nickel-Komplexe

During studies on the mechanism of ligand displacement reactions of nickelocene non-ionic monocyclopentadienylnickel complexes of the type π? C₅H₅Ni[P(OP)₃]X with X = Cl and P(O) (OR)₂ have been obtained. The new compounds have been characterised by means of their IR., UV., NMR. and Mass spectroscopic data. The phosphonate ligands are bonded with the phosphorus atom to the transition metal.     

Zur Synthese von Homocamphenilansäure

Syntheses of the title compound and of some of its derivatives are described. Homocamphenilanic acid could not be obtained by aDiels-Alder reaction of cyclohexadiene with an appropriate dienophile but is easily accessible via homocamphene by hydroboration of this homoterpene and subsequent oxidation of the reaction product.

Anmerkung: Zur Verwendung der Vorsilbe Homo- im Zusammenhang mit Norbornanen siehe Lit. [13] und Fußnote in Lit. [12].     

Metallaheterocumulene : III. Ungewöhnliche bildung von (CO)5Cr=C=NCPh2N=C=Cr(CO)5 bei der reaktion von [(CO)5Cr=C=N=CPh2] AlBr4 mit tetrahydrofuran

Pentacarbonyl(3,3-diphenyl-2-azaallenylidene)chromium tetrabromoaluminate, [(CO)₅Cr=C=Nz.dbnd;CPh₂]⁺ AlBr₄⁻, reacts with THF in dichloromethane to give the dinuclear bis(isonitrile) complex [(CO)₅Cr=C=N]₂CPh₂ which formally corresponds to the product of a reductive dimerization of two [(CO)₅Cr=C=N=CPh₂]⁺ moieties with concomitant elimination of one CPh₂ fragment.     

On the hyperbolicity of Einstein's and other gauge field equations

It is shown that Einstein's vacuum field equations (respectively the conformal vacuum field equations) in a frame formalism imply a symmetric hyperbolic system of reduced propagation equations for any choice of coordinate system and frame field (and conformal factor). Certain freely specifiable gauge source functions occurring in the reduced equations reflect the choice of gauge. Together with the initial data they determine the gauge uniquely. Their choice does not affect the isometry class (conformal class) of a solution of an initial value problem. By the same method symmetric hyperbolic propagation equations are obtained from other gauge field equations, irrespective of the gauge. Using the concept of source functions one finds that Einstein's field equation, considered as second order equations for the metric coefficients, are of wave equation type in any coordinate system.Work supported by a Heisenberg-Fellowship of the Deutsche Forschungsgemeinschaft     

Calcium phosphate colloids with hierarchical structure controlled by polyaspartates

 Precipitation of calcium phosphate in a double-jet experiment in the presence of sodium polyaspartic acid results in a structural evolution of stable colloidal objects with a variety of unconventional morphologies. This structural evolution is characterized by a combination of techniques, namely static and dynamic light scattering, small-angle and wide-angle X-ray scattering, and transmission electron microscopy. It is shown that after immediate formation of amorphous precursor nanoparticles with a “parachute architecture”, the system transfers into a hollow sphere morphology in the 500-nm region and is composed of plateletlike nanocrystals, and again is transferred into a final, “snowball-like” morphology of high structural definition and monodispersity. The kinetics depends on the amount and the molecular weight of the polymer, but similar structural elements are found in all the cases examined. When repeated in a triple-jet experiment, which also ensures a constant polymer concentration, it was possible to intercept a postulated intermediate structure in practically complete yield, namely crystalline hydroxyapatite nanofibres with extremely high axial ratios which form an interwoven gel. Received: 11 May 2001 Accepted: 14 September 2001     

Novel initiating systems for the living polymerization of acrylates and methacrylates

The polymerization of methyl methacrylate with lithiated initiators in the presence of aluminium alkyls in toluene has living character but it deviates from conventional first-order kinetics and the polymers have fairly broad molecular weight distributions. This results from the formation and precipitation of a coordinative polymer network in which the lithium ions of the living chain ends are coordinated to the in-chain ester carbonyl groups. Thus, the network formation can be prevented by adding Lewis bases like methyl pivalate which coordinate to the living chain ends instead of the polymer. Alternatively, one can introduce tetraalkylammonium salts aiming at an exchange of the lithium ion by a less electropositive cation. Both approaches lead to linear first-order time conversion plots for the polymerization of methacrylates and acrylates and to narrow molecular weight distributions, i.e., to a living and controlled polymerization. With these new initiating systems, various block and graft copolymers can be synthesized.