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.     

Investigations of precipitates in heat treated AgPd30/CuSn6 layers

The subject of the investigations are precipitation zones, which grew as a result of chemical diffusion in AgPd30/CuSn6 bimetals. These precipitation zones have been characterized by metallography, electron probe microanalysis and x-ray diffraction. The growth of precipitation zones in the plating layer and in the substrate layer in dependence on time have been determined. The use of x-ray diffraction alone for the identification of the precipitates could not supply satisfying results in every case. This problem was solved by the application of electron probe microanalysis using a correction method, which allows the estimation of the chemical composition of small particles.Dedicated to Professor Dr. rer. nat. Dr. h. c. Hubertus Nickel on the occasion of his 65th birthday     

Study of the development of thermoresistance in human pancreatic carcinoma cell lines using proteome analysis

In order to find candidate proteins that are potentially associated with the thermoresistant phenotype in combination with drug resistance, we analyzed the differential protein expression in vitro in the human pancreatic cancer cell line EPP85-181-P and classical and atypical multidrug-resistant variants and their thermoresistant counterparts using proteomics. This study identifies sets of proteins that may lead to the development of thermoresistance. These results provide a fundamental basis to elucidate the molecular mechanism of thermoresistance and chemoresistance phenomena that may assist the therapy of inoperable cancers.     

Model Reactions for Photosynthesis—Photoinduced Charge and Energy Transfer between Covalently Linked Porphyrin and Quinone Units

Photosynthesis is one of the fascinating fields of current interdisciplinary research. It seems miraculous that nature, in the process of evolution, has managed to bring about the process of photosynthesis. The first step involves a charge separation at the reaction centers, which proceeds with 100% quantum yield from the photoexcited singlet state of the bacteriochlorophyll donor, despite the fact that the wasteful deactivation of the electron into the ground state should be highly favored. Biomimetic model compounds (that is, those which resemble the pigments nature has developed) have been constructed from porphyrins and quinones. These model systems have allowed the study of the factors contributing to the highly efficient charge separation. This report focuses on recent developments in the study of electron transfer in porphyrinoquinones. Some of the results of these investigations may not be not fully understood and are often the subject of controversial discussions.     

Quantitative validation of different protein precipitation methods in proteome analysis of blood platelets

For the preparation of proteins for proteome analysis, precipitation is frequently used to concentrate proteins and to remove interfering compounds. Various methods for protein precipitation are applied, which rely on different chemical principles. This study compares the changes in the protein composition of human blood platelet extracts after precipitation with ethanol (EtOH) or trichloroacetic acid (TCA). Both methods yielded the same amount of proteins from the platelet preparations. However, the EtOH-precipitated samples had to be dialyzed because of the considerable salt content. To characterize single platelet proteins, samples were analyzed by two-dimensional fluorescence differential gel electrophoresis. More than 90% of all the spots were equally present in the EtOH- and TCA-precipitated samples. However, both precipitation methods showed a smaller correlation with nonprecipitated samples (EtOH 74.9%, TCA 79.2%). Several proteins were either reduced or relatively enriched in the precipitated samples. The proteins varied randomly in molecular weight and isoelectric point. This study shows that protein precipitation leads to specific changes in the protein composition of proteomics samples. This depends more on the specific structure of the protein than on the precipitating agent used in the experiment.     

Die Kristallstruktur von wasserfreiem Melaminiumchlorid

Crystal Structure of non‐aqueous Melaminium Chloride Melaminium chloride was obtained as colorless, needle‐shaped, single crystalline material from solid state reactions between melamin and ammonium chloride. The structure of [C₃N₆H₇]Cl was refined by single crystal X‐ray diffraction: I2/m, Z = 8, a = 852.87(4), b = 1704.4(1) c = 918.44(4) pm and β = 92.165(6)°. The crystal structure contains melaminium ions stacked to columns along [100] and linked via N‐H···N bridges to form bands along [001]. Both of the two distinct chloride ions are stabilized by six hydrogen bonds through distorted trigonal prismatic arrangements of hydrogen atoms to yield a supramolecular structure.     

A new tripodal receptor for molecular recognition of monosaccharides. A paradigm for assessing glycoside binding affinities and selectivities by 1H NMR spectroscopy

A new tripodal receptor for the recognition of monosaccharides is described. The prototypical host 1 features a 1,3,5-substituted 2,4,6-triethylbenzene scaffold bearing three convergent H-bonding units. The binding ability of the t-octyl derivative 1a toward a set of octylglycosides of biologically relevant monosaccharides, including Glc, Gal, Man, and GlcNAc, was investigated by 1H NMR in CDCl3. A protocol for the correct evaluation of binding affinities was established, which can be generally applied for the recognition of monosaccharides by 1H NMR spectroscopy. A three-constant equilibrium model, including 1:1 and 2:1 host-guest association and dimerization of the receptor, was ascertained for the interaction of 1a with all the investigated glycosides. An affinity index, which we defined median binding concentration BC50 in analogy to the IC50 parameter, intended to address the general issue of comparing dimensionally heterogeneous binding data, and a limiting BC0(50)quantity describing intrinsic binding affinities were developed for evaluating the results. BC0(50) values for 1a range from 1 to 6 mM, indicating an intrinsic binding affinity in the millimolar range and a selectivity factor of 5 toward the investigated glycosides. The treatment has been extended to include any generic host-guest system involved in single or multiple binding equilibria.     

Probing the glycosidic linkage: UV and IR ion-dip spectroscopy of a lactoside

The beta(1-->4) glycosidic linkage found in lactose is a prevalent structural motif in many carbohydrates and glycoconjugates. Using UV and IR ion-dip spectroscopies to probe benzyl lactoside isolated in the gas phase, we find that the disaccharide unit adopts only a single, rigid structure. Its fully resolved infrared ion-dip spectrum is in excellent agreement with that of the global minimum structure computed ab initio. This has glycosidic torsion angles of phi(H) (H1-C1-O-C4') approximately 180 degrees and psi(H) (C1-O-C4'-H4') approximately 0 degrees which correspond to a rotation of approximately 150 degrees about the glycosidic bond compared to the accepted solution-phase conformation. We discuss the biological implications of this discovery and the generality of the strategies employed in making it.     

The Molecular and Crystal Structure of the Glycopeptide A-40926 Aglycone

The crystal structure of a glycopeptide antibiotic A–40926 aglycone was investigated by X-ray analysis at ?120°. A-40926 crystallises in the orthorhombic space group P2₁2₁2₁ with two monomers in the asymmetric unit, a = 21.774(4), b = 28.603(7), c = 29.757(4) Å. ‘Conventional’ direct methods approach failed to solve the structure, but a novel iterative real/reciprocal space procedure was successful. Refinement against 11248 F² data led to R1 = 13.3% for 6770 F > 4σ (F). The two monomers of A-40926 have similar conformations and are bound by antiparallel H-bonds to form a ‘chain’ structure of connecting dimers. The antibiotic molecule possesses a ‘binding pocket’ for the C-terminal carboxy group of the cell-wall protein, which is consisten with suggestions based on NMR data and the recently reported crystal structure of ureido-balhimycin. In A-40926 the monomers are polymerically linked by H-bonds, quite unlike the tight dimer formation observed in ureido-balhimycin.