Stereochemie vonGrignard-Reaktione mit 2-(N-Methylanikino)-cyclopentanonen

TheGrignard reactions of the 2-anilinocyclopentanones (1 a and1 b) with CH₃MgI and C₆H₅CCMgBr, giving the 2-anilinocyclopentanols2 a, 2 b, and2 c, and the synthesis oftrans-1-methyl-2-(4-chloro-N-methylanilino)-cyclopentanol (4), which was used as a reference compound of known stereochemistry, are described. IR spectroscopic investigations of2 a, 2 b, and2 c as compared with4 lead to the conclusion that2 a, 2 b, and2 c have the structures ofcis-2-(N-methylanilino)-cyclopentanols.     

Kontrastumkehr im Elektronen-Emissions-Mikroskop

In an emission microscope in which the image forming secondary electrons are emitted under bombardment with 15 kev primary electrons, variations of contrast during observation are found. In the image of the surface of a ZnAl alloy which is kept at room temperature in a vacuum of 10^?4 tor, the contrast changes its sign during observation. It is shown that this phenomenon is due to a hydrocarbon polymeride layer growing on the surface. The emissivity of Al which originally exceeds that of Zn, is reduced by the contamination faster than that of Zn. First, the brightness of the surface regions consisting of Al are brighter than those of Zn, after some time both emit with equal brightness, then Zn emits stronger, and at last all parts of the surface give an equal emission corresponding to the hydrocarbon polymeride. Experiment with Al-Zn and Al-Au specimens confirm this explanation.     

Homopolymerization of ethylene, 1-hexene, styrene and copolymerization of styrene with 1,3-cyclohexadiene using (η⁵-tetramethylcyclopentadienyl)dimethylsilyl(N-Ar')amido-TiCl₂/MAO (Ar'=6-(2-(diethylboryl)phenyl)pyrid-2-yl, biphen-3-yl)

The propensity of a half-sandwich (η?-tetramethylcyclopentadienyl) dimethylsilylamido Ti(IV)-based catalyst bearing an auxiliary diethylboryl-protected pyridyl moiety (Ti-8), activated by methylaluminoxane (MAO) to homopolymerize α-olefins such as ethylene, 1-hexene and styrene as well as to copolymerize styrene with 1,3-cyclo-hexadiene is described. The reactivity of Ti-8 was investigated in comparison to a 6-(2-(diethylboryl)phenyl)pyrid-2-yl-free analogue (Ti-3).     

Copper-O2 reactivity of tyrosinase models towards external monophenolic substrates: molecular mechanism and comparison with the enzyme

The critical review describes the known dicopper systems mediating the aromatic hydroxylation of monophenolic substrates. Such systems are of interest as structural and functional models of the type 3 copper enzyme tyrosinase, which catalyzes the ortho-hydroxylation of tyrosine to DOPA and the subsequent two-electron oxidation to dopaquinone. Small-molecule systems involving μ-η2:η2 peroxo, bis-μ-oxo and trans-μ-1,2 peroxo dicopper cores are considered separately. These tyrosinase models are contrasted to copper-dioxygen systems inducing radical reactions, and the different mechanistic pathways are discussed. In addition to considering the stoichiometric conversion of phenolic substrates, the available catalytic systems are described. The second part of the review deals with tyrosinase. After an introduction on the occurrence and function of tyrosinases, several aspects of the chemical reactivity of this class of enzymes are described. The analogies between the small-molecule and the enzymatic system are considered, and the implications for the reaction pathway of tyrosinase are discussed (140 references).     

Immobilization and AFM of single 4 x 6-mer tarantula hemocyanin molecules

The high molecular mass respiratory protein of the tarantula Eurypelma californicum, a 4 × 6-mer hemocyanin, was investigated by atomic force microscopy (AFM). Various substrates and methods were evaluated for immobilization of individual hemocyanin molecules on a solid surface. Samples were imaged after physisorption on mica and self-assembled monolayers, and after chemisorption on Au(111) and N-hydroxy-succinimide (NHS) functionalized surfaces. AFM measurements were carried out preferable in solution and contact mode, but also in Tapping mode and on air-dried samples. Adsorption of the protein on mica followed by drying and carrying out the measurements in Tapping mode gave the best results. In the AFM images the four hexamers of the native 4 × 6-mer hemocyanin have been defined. The results were compared with independent available structural data and represent a validation case for this technique applied for the first time on such giant and complex molecules. As observable in images taken by transmission electron microscopy and also proposed from SAXS data, 4 × 6-mers could be found where the half-molecules are tilted against each other. This study is a step in resolving conformational heterogeneities, involved in oxygen binding of hemocyanins, at the single-molecule level by AFM.