Solvothermale Synthese und Bestimmung der Kristallstrukturen von AgBiI4 und Ag3BiI6

Solvothermal Synthesis and Crystal Structure Determination of AgBiI₄ and Ag₃BiI₆ AgBiI₄ and Ag₃BiI₆ were synthesized by solvothermal reaction from AgI and BiI₃ in diluted HI‐solution (20 %) at a temperature of 160 °C. The greyish‐black crystals grow as octahedra (AgBiI₄) or hexagonal/trigonal platelets (Ag₃BiI₆). AgBiI₄ crystallizes in space group Fd3¯m with a = 1222.3(1) pm (300 K) and Z = 8 whereas Ag₃BiI₆ shows the space group R3¯m with a = 435.37(6) pm, c = 2081.0(4) pm (300 K) and Z = 1. Both crystal structures show stacking sequence abcabc… of hexagonal layers containing Iodine. Bismuth and silver are sharing octahedral sites with different mass ratio in both structures. The part of silver which could be localized varies with temperature. This behaviour indicates mobility of silver within the crystal structure. The ionic conductivity of AgBiI₄ is explored. AgBiI₄ and Ag₃BiI₆ show close structural relationship, with AgBiI₄ as a variant with a higher degree of order.     

Synthesis of CoFe2O4 nanowire in carbon nanotubes. A new use of the confinement effect

Cobalt ferrite nanowires with an average diameter of 50 nm and lengths up to several micrometers were synthesized inside carbon nanotubes under mild reaction conditions using the confinement effect provided by the carbon tubular template.     

Vibrational spectra of Hg3TeO6 and Hg2TeO5

The infrared and Raman spectra of the crystalline hexaoxotellurates Hg3TeO6 and Hg2TeO5 were recorded and discussed on the basis of a site symmetry analysis derived from known structural data. Approximate values for the Te-O bond force constants are reported and some comparisons with related species are made.     

Investigation of homo- and heterodimer alkali metal cation complexes of resorc[4]arenes by electrospray ionization mass spectrometry

Resorc[4]arenes are compounds with interesting properties, mainly because of their ability to form host-guest complexes with the guest located inside the cavity. The size of the guest limits the complexation, as shown by a competition experiment with tetraalkylammonium ions of different size. By electroscopy ionization tandem mass spectrometric experiments on resorc[4]arene heterodimers bearing an alkali metal ion as guest, it was found that there must be two different binding mechanisms for alkali metal ions with high surface charge density (Li(+) and Na(+)) on the one hand compared with those with a lower surface charge density on the other hand (K(+), Rb(+), Cs(+)).     

Theory of measurement of gas-adsorption equilibria by rotational oscillations

The gas adsorbed on the inner surface of a highly porous material like activated carbon or zeolite can be measured by slow damped oscillations of a torsional pendulum. The physical principles and the theory of this method are outlined. Formulas are given relating the increase in mass due to adsorption to changes of the frequency and the logarithmic decrement of slow, damped rotational oscillations of the pendulum. Preliminary measurements of gas adsorption equilibria of nitrogen on activated carbon show that the ratio of the mass adsorbedm, to the mass of the adsorbentm ^s , can be determined by this method with mean absolute error |m/m ^s |0.04%.Dedicated to the memory of Joseph Kestin (1913–1993).     

Reinvestigation of the Conformation of Cyclosporin A in Chloroform

New investigations of cyclosporin A in CDCl₃ have been performed to obtain additional and more accurate distance restraints than utilized in our previous studies of cyclosporin A. Build-up rates at 600 MHz using 6 different mixing times at low temperatures (252.5 K) were determined and transformed into distances using the two-spin approximation. With the new distance restraints in the MD simulations using the GROMOS package, we can unambiguously conclude the presence of a βII′-turn. The new structure resembles the X-ray structure more than the structure previously determined, especially regarding the orientation of the MeBmt side chain. In the new structure and in the solid state, the side chain is folded over the backbone (although there are substantial differences in the χ₁ torsion), in contrast to the old structure, where the side chain is extended away from the backbone.     

Synthesis of enantiopure axially chiral C3-symmetric tripodal ligands and their application as catalysts in the asymmetric addition of dialkylzinc to aldehydes

The enantioselective synthesis of a novel-type C(3)-symmetric tripodal ligand that is composed of a central mesitylene-derived core and three functionalized, axially chiral biaryl subunits is described. The triol (M,M,M)-3 is a suitable catalyst for the enantioselective addition of dialkylzinc to various aromatic aldehydes with asymmetric inductions of up to 98% ee.     

Stereochemistry of isoplagiochin C, a macrocyclic bisbibenzyl from liverworts

Cyclic bisbibenzyls, like isoplagiochins C (1) and D (2), are stereochemically intriguing molecules: Although not equipped with any of the traditional stereogenic elements that render molecules conformationally stable per se, they are sometimes isolated in an optically active form and are thus chiral at room temperature. The paper describes quantum chemical calculations, in particular investigations of the conformational space and molecular dynamics simulations, showing that the helicity is a property of the entire molecule, whose ring strain makes the molecule configurationally stable overall, with (formally) three stereogenic elements (two biaryl axes and one helical stilbene unit). Only one of the biaryl axes (the 'upper' one, joining C-12' and C-14) has a stable configuration, leading to a population of four interconverting diastereomers, yet without racemization at room temperature. On the basis of these conformational and dynamic calculations, the circular dichroism spectrum of isoplagiochin C (1) was calculated, leading to the first assignment of the absolute configuration of a cyclic bisbibenzyl. Accordingly, 1 has the P-configuration at the stereochemically stable biaryl axis and constitutes a mixture of diastereomers with respect to the other biaryl axis and the helical stilbene unit. From the temperature dependence of the racemization rates, an enantiomerization barrier of 101.6 kJ/mol was determined. Likewise, for the first time for cyclic bisbibenzyls, the enantiomeric ratio of this natural product was determined, by chromatography on a chiral phase with CD-coupling. Accordingly, 1 from Plagiochila deflexa is not enantiomerically pure, but occurs in a 85:15 ratio in favor of the enantiomer that has the P-configuration at the stereochemically stable axis.     

Matrix-assisted laser desorption/ionization mass spectrometry with additives to 2,5-dihydroxybenzoic acid

Selected benzoic acid derivatives and related substances were used as additives to 2,5-dihydroxybenzoic acid (2,5DHB) and the performance of the mixtures in matrix-assisted laser desorption/ionization mass spectrometry was investigated. Using benzoic acid derivatives substituted at position 2 and/or 5 or related substances as a co-matrix in the 1–10% range with 2,5DHB results in improved ion yields and signal-to-noise ratio of analyte molecules, especially for the high-mass range. The enhanced performance is prominent for 2-hydroxy-5-methoxybenzoic acid and exists for both proteins and oligosaccharides. It is suggested that the improvement is caused by a disorder in the 2,5DHB crystal lattice allowing ‘softer’ desorption. Charge transfer from matrix ions to additive molecules at the expense of analyte ionization gives a simple explanation for the deteriorating effects of some tested additives.     

A fluorimetric assay for cortisol

A simple, rapid and sensitive fluorimetric assay for the quantitative determination of cortisol is reported. The assay is based on the formation of a fluorescent dye when cortisol is incubated with a mixture of sulfuric acid and acetic acid. The fluorescence spectrum recorded for the resulting dye shows a maximum extinction at 475 nm and a maximum emission at 525 nm. The solvent 2-methyl-4-pentanone was used for extraction and was found to act as a fluorescence amplifier. A limit of detection of 2.7 μM was achieved, making it possible to forego solvent evaporation. The assay suffers minor interference from 11-deoxycortisol which exhibits low fluorescence at λ _ex: 460 nm; λ _em: 505 nm. Typical standard deviations were below 4%. We validated the assay using a biotransformation with recombinant Schizosaccharomyces pombe which regioselectively hydroxylates 11-deoxycortisol to cortisol. The method described herein is suitable for preliminary screening of microorganisms capable of steroid hydroxylation.