Diels-Alder-Reaktionen von Vinylindolen mit Arin und 1,4-Benzochinonen: Neue potentielle DNA-Interkalatoren

Summary Diels-Alder reactions of 2- and 3-vinylindoles with aryne, 1,4-benzo- and 1,4-naphtho-quinone lead to new six-ring annellated carbazoles. Molecular modeling studies predict that the compounds with coplanar framework are able to intercalate with the B-DNA.

     

Burning of thermally thin polyethylene mixtures

The burning of polyethylene in the mixture with aluminium hydroxide, aluminium oxide, cellulose and Irganox 1010 has been examined by cone calorimeter under non-standard sizes of the sample. The time to ignition of pure polyethylene decreases with decreasing initial amount of polyethylene powder. The subtraction of the mass of water released from the total mass lost for polyethylene with aluminium hydroxide give the same values of effective heats of combustion as for pure polyethylene up to the load about 50 mass% of aluminium hydroxide. The mean heats of combustion determined from the cone calorimeter software are higher than those determined from the total oxygen consumed and mass lost multiplied by the factor 13.1. The additivity rule was found for effective heat of combustion and total smoke released for polyethylene with cellulose. The free radical scavenger Irganox 1010 does not show a significant effect on the flammability of polyethylene except for the increase of the total smoke released. The equation describing the heat release rate evolution in time has been proposed showing a good fit to the experimental runs.     

N-heterocyclic carbenes as ligands in high-valent molybdenum and tungsten complexes

Oxometal complexes of molybdenum and tungsten in high oxidation states from stable adducts with 1,3-dimethylimidazoline-2-ylidene (L) 1. The first ‘carbene’ complexes of molybdenum(VI) [MoO₂Cl(L)₃]Cl (3a) and tungsten(VI) WO₂Cl₂(L)₂ (4b) are reported.     

Asymmetric benzoin reaction catalyzed by benzoylformate decarboxylase

Aromatic aldehydes are converted into benzoins by benzoylformate decarboxylase catalyzed C–C bond formation. The reaction affords (R)-benzoins with high enantiomeric excess and in good chemical yields. A broad range of aromatic aldehydes can be used as substrates in aqueous buffer or buffer/DMSO-solutions.     

Ceramic Foams from a Preceramic Polymer and Polyurethanes: Preparation and Morphological Investigations

Open-cell ceramic foams were obtained from a preceramic polymer (silicone resin) and blown polyurethanes. The preceramic polymer, which is crosslinked by condensation of silanol groups, was dissolved in CH2Cl2 and added to a liquid polyol containing the surfactant and the amine catalyst. Isocyanate was then added to the mixture and the foam was obtained through a twofold blowing mechanism (physical and chemical blowing). The morphology of the expanded polyurethane, which can be flexible or semirigid, characterized the final structure of the ceramic foam. The materials obtained were pyrolyzed in a nitrogen flux at temperatures of 1000–1200°C, thus allowing for the polymer-to-ceramic transformation to occur in the preceramic polymer. The ceramic foams produced in this way consisted of an amorphous silicon oxycarbide ceramic (SiOC). They presented a density ranging from 0.1 to 0.3 g/cm3. The average pore diameter ranged from 200 to 400 m and they possessed 80 to 90% open porosity.