Atom-probe field ion microscopy

The atom probe field ion microscope (AP-FIM) is a combination of a field ion microscope and a time-of-flight mass spectrometer with a single ion detection sensivity. With the field ion microscope topology of a surface, surface reactions and surface modifications can be studied in atomic detail. By time-of-flight measurements surface layers and interface layers can be chemically analyzed atom by atom and atomic layer by atomic layer. Compositional variations according to surface or interface segregation, precipitations, or surface changes in corrosion or in electrochemical layer formation etc. can be studied quantitatively on a subnanometer scale. Some of our studies on related problems will be decribed briefly.     

Photochemical structuring and fixing of structures in binary polymer brush layers via 2pi+2pi photodimerization

Binary polymer brushes grafted to Si wafers were prepared from hydrophilic and hydrophobic polymer components, which allow switching the surface properties (as revealed by contact angles) by exposure to varying solvents. The hydrophilic component was poly-2-vinylpyridine; the hydrophobic component was a copolymer of styrene and 2-(4-vinylphenyl)indene containing the photodimerizable phenylindene chromophore. The brushes were prepared via thermal and via photochemical grafting-to methods, which led to distinct layer thicknesses. Structural patterns differing in surface properties were produced and fixed via crosslinking the hydrophobic component by 2pi+2pi photodimerization of phenylindene moieties. The patterns were visually observable.     

Protein Prenylation: An (Almost) Comprehensive Overview on Discovery History, Enzymology, and Significance in Physiology and Disease

Summary. Since 1979, when prenylation has been first discovered as chemical oddity of a yeast mating factor, the two forms of this posttranslational modification of proteins (farnesylation and geranylgeranylation) have been found as wide spread among proteins from Eukarya and their viruses. This review attempts to summarize as comprehensively as possible the enzymological processes of prenylation and the various aspects of their biological significance. The substrate proteins of prenyltransferases are known to carry a sequence signal composed of a cysteine-containing 4–5 residue stretch at the utmost C-terminal end that is N-terminally preceded by a flexible and polar linker region of ca. 10 residues. Postprenylation processing of substrate proteins can involve C-terminal proteolysis, C-terminal carboxyl methylation, and other steps of maturation. The prenyl anchor functions as module for membrane attachment or for protein–protein interaction. Prenyl anchor carrying proteins fulfill a large array of functions in signaling and regulation of cellular processes. Therefore, they are involved in the pathogenesis of a variety of human diseases, the most prominent one being cancer. Farnesyltransferase inhibitors show surprisingly high efficiency in controlling tumor growth in model systems but, so far, clinical trials with human patients have remained without the desired success. Interference into prenylation pathways appears also a promising treatment principle in a variety of parasitic diseases.     

Synthese von 15-Hydroxy[9]metacyclophan

Synthesis of 15-Hydroxy[9]metacyclophane 3-(1-Nitro-2-oxocyclododecyl)propanal ( 1 ) was converted to 15-hydroxy[9]metacyclophane ( 3 ) on two different routes. In the first case the internal aldol reaction product of 1 was treated with K₂CO₃/THF to give 3 in 29 % yield with regard to cyclododecanone. Alternatively, the aldehyde 1 reacted with a primary amine to form e.g. 4 which gave 3 in the presence of CH₃I/K₂CO₃ in 48 % yield.     

Phospholipid mesophases at solid interfaces: in-situ X-ray diffraction and spin-label studies

In this work, we report on recent investigations, both on the global and on the local molecular architecture of supported phospholipid model membranes. A brief theoretical introduction explains how global structural information on supramolecular lipid ensembles can be retrieved from surface X-ray diffraction measurements as well as how spin-label electron paramagnetic resonance spectroscopy (EPR) provides complementary information on the local environment of probe molecules. The combination of especially designed X-ray cells with the technique of small- and wide-angle X-ray surface scattering makes it possible to explore various fields of lipid research and its applications. Examples for different physico-chemical conditions are presented: (i) in situ chemistry under excess of water conditions demonstrating how solid-supported lipid films sense salinity, (ii) the 3D electron density reconstruction of a vesicle-fusion intermediate under controlled humidity, and (iii) complementary temperature and pressure effects on oriented phospholipid samples. Further, special attention has been given to the influence of different film preparation techniques with respect to quality and the defect structure manifestation. To resolve the proportions and local properties of defects in a hydrated lipid-deposited surface, spin-label EPR was applied. The results from 9.6 GHz EPR as well as from 1.2 GHz EPR suggest the alignment to be in the range between 30% and 80%. In addition, slow time-dependent EPR measurements point to nano-structural rearrangements due to water flow and reduction of alignment quality.