Die kristall- und molekülstruktur von Fe3Te2(CO)9

The crystal and molecular structure of Fe₃Te₂(CO)₉ has been determined by X-ray diffraction analysis. The compound crystallizes in the triclinic space group P$\text{1}$ with a 952.5(4), b 1314.3(8), c 694.7(2) pm, α 95.27(4), β 112.78(3), γ 81.44(4)° and Z = 2 (R = 0.036, using 2079 reflections).     

Structural Efficiency and Microstructural Modeling of Wet Gels and Aerogels

We present a microstructural model of aerogels that includes the effect of particle necks, tortuosity and dangling ends on the scaling of elastic moduli with density. Relative neck radii can be determined for sintering series of silica aerogels and for Resorcinol Formaldehyde (RF) aerogels produced with different catalyst concentrations. The density of elastically ineffective dangling ends and the tortuosity can be estimated using information from thermal conductivity and elastic modulus measurements in silica aerogels. Typical values for the load bearing mass range from >50% for high density and heat treated aerogels to <10% of the total mass for low density wet-gels.     

Observation of a rectangular columnar phase in a DNA-calcium-zwitterionic lipid complex

In the presence of calcium, DNA and unilamellar liposomes of the zwitterionic lipid DPPC form a complex in which DNA strands are embedded between a lamellar phase of DPPC. In some complexes, in-plane alignment of the DNA strands occurs, where a DNA-DNA interaxial distance can be measured using small-angle X-ray scattering. Here we report a higher level of DNA organization, with a rectangular columnar phase of DNA identified within this complex structure. This observation is important in view of recent interests in creating new synthetic systems at the interface of biology.     

Synthesis of a phosphine-modified cyclodextrin and its rhodium complex

A bidentate ligand consisting of a 2-(diphenylphosphinoethyl)-thio moiety was attached to β-cyclodextrin at the 6-position. The corresponding norbornadiene Rh(I) complex in the form of the BF₄⁻ salt was prepared.     

The Isocyanide–Cyanide Rearrangement; Mechanism and Preparative Applications

Until recently the isocyanide–cyanide rearrangement was of interest almost solely as an example of a unimolecular gas-phase reaction, and kinetic studies had been carried out in only a few simple cases. Kinetic measurements in solution were made possible only by the discovery and suppression of a parallel free-radical chain process which leads to the same products. The rate of the isomerization is almost independent of the structure of the starting material and of the substituents present. An exception is provided by extreme steric hindrance in three dimensions which, as in tris-α-substituted triptycyl isocyanides, leads to a considerable increase in the activation energy. The results can be interpreted in terms of a purely sigmatropic mechanism, as predicted by ab initio calculations. The preparative application of this rearrangement reaction requires the suppression of side reactions and can best be carried out by flash pyrolysis; yields are then almost quantitative. Allyl isocyanides react without allyl isomerization, optically active isocyanides with complete retention of configuration. New, economically interesting syntheses for the known nonsteroidal anti-inflammatory drugs ibuprofen and (S)-naproxene are described. The application of the useful synthetic building blocks, the optically active β-acyloxy cyanides, which are formed from optically active α-amino acids, will be demonstrated.     

Improved procedure for the synthesis of thiazolium-type peptide coupling reagents: BMTB as a new efficient reagent

An efficient scalable synthesis of 2-halothiazolium-type peptide coupling reagents has been developed. The key step is the formation of the 2-bromothiazole scaffold through cyclization of α-thiocyanato ketones with hydrogen bromide. Using this method, the new coupling reagent 2-bromo-N-methylthiazolium bromide (BMTB) was synthesized. BMTB was tested in a difficult model coupling reaction of two sterically hindered N-methylated amino acids and showed higher activity than the well-established peptide coupling reagent HATU.