First hint on a change of the 210Po alpha-decay half-life in the metal Cu

In the metal Cu cooled to T = 12K the α-decay half-life of ²¹⁰Po nuclides, located inside the metal, was measured to be shorter by 6.3±1.4% compared to that at room temperature.     

Flow control over an undulating membrane

The flow along a flexible membrane forced to undulate in the form of a streamwise travelling wave pattern is studied experimentally in detail. Flow field and force measurements confirm that the form drag of the wavy wall is significantly reduced when starting the undulatory motion. A mechanical model of an undulating membrane was built, based on previous investigations described in literature, and placed in an open water channel. The motion pattern of the membrane was prescribed in such a way to achieve a downstream travelling wave with increasing amplitude. The exploratory focus laid on the identification of hydrodynamic mechanisms of drag reduction due to undulatory motion. The wave-speed c of the travelling wave was set proportional to the incoming flow velocity U, according to an optimum ratio identified by previous numerical and experimental investigations. Poisson’s equation for the pressure was used to calculate the 2D pressure field from the experimental data of the unsteady flow field. In addition, the integral drag force of the membrane, as a function of c/U, was measured with a force balance to compare with previous published numerical findings. Furthermore, the velocities close to the surface of the membrane were measured, and the boundary layer profiles were determined. The resulting normalised velocity profiles affirm an oscillation between laminar and turbulent flow over one period of the motion. The results are in good agreement with previous experimental and numerical findings. Additionally, the characteristics of the flow along a travelling wave with increasing amplitude are discussed in more detail.     

Self-localization of polyacrylic acid molecules on polar ZnO(0001)-Zn surfaces

The adsorption of single polyacrylic acid (PAAc) molecules was investigated on stepped hydroxide-stabilized polar ZnO(0001)-Zn surfaces using atomic force microscope (AFM) topography and force distance spectroscopy. Stepped surfaces of ZnO(0001)-Zn were prepared by a wet chemical etching procedure and PAAc molecules were adsorbed from aqueous NaClO(4) solutions. AFM single molecule topography studies could be utilized to show that polyacrylic acid molecules specifically adsorb on the non-polar (10-10) step edge faces at low ionic strengths. The radius of gyration of the dissolved PAAc in aqueous solution was measured by means of static light scattering experiments yielding a radius of gyration of R(g)=136 nm at pH 7.4 in 50 mM NaClO(4)/NaOH solution, which is in good agreement with the size of the adsorbed PAAc molecules as measured using AFM. The obtained results could be rationalized in terms of binding-site configurations at step edges and the effect of the chemical environment on both local electric double layer charge and molecular conformation of the PAAc molecules. The point of zero charge of the ZnO(10-10) surface was measured with chemical force microscopy to be pH(PZC)=10.2 ± 0.2. The specific adsorption of polyacrylic acid at non-polar ZnO step-edges can be explained by coordinative bonds formed between the carboxylic acid group and the Zn-surface atoms. On the hydroxide stabilized polar surface only weak hydrogen bonds can be formed in addition to van-der-Waals forces. Thus a "diffusion and trapping" mechanism keeps the adsorbed PAAc molecules mobile on the ZnO(0001)-Zn surface terraces due to small interaction forces until they are trapped at the (10-10) step faces by stronger coordinative bonds from the carboxylic groups to zinc atoms located in the first atomic layer of the crystal structure.     

Yeasts as Producers of Polyhydroxyalkanoates: Genetic Engineering of Saccharomyces cerevisiae

The genes of the poly(β-hydroxybutyrate) (PHB) synthesis pathway in Ralstonia eutropha and Methylobacterium extorquens were successfully established in the yeast Saccharomyces cerevisiae. Expression of just the polyhydroxyalkanoate (PHA) synthase gene in some experiments, and all three PHB genes (i.e., the genes encoding β-ketothiolase, acetoacetyl-CoA reductase, and PHA synthase) in others, were detected in S. cerevisiae. Thus, it can be used as a “cell factory” for the production of PHB. The maximum amount of polyester accumulated was 6.7% (wt./wt.) when all three genes were expressed. The amount of polymer accumulated in the transgenic yeast harboring just the PHA synthase gene was similar (5.2%), but slightly lower, indicating the necessity of expressing all three genes for high PHB contents in the cells. For viable production of the polymer in yeasts, more needs to be learned about the metabolism of the yeast, especially about the pathways and intermediates competing with formation of the biopolymer. Another host probably needs to be chosen.

Bacteria (on the top) with PHB inclusions and yeasts with storage compounds (on the bottom).     

Synthesis of new calix[4]arene‐based phosphorus ligands and their application in the Rh(I) catalyzed hydroformylation of 1‐octene

The synthesis of calix[4]arene‐based phosphorus diamides and phosphites is described. These oligocyclic ligands have been tested in the Rh(I)‐ catalyzed hydroformylation of 1‐octene. Depending on the reaction conditions, yields up to 99% and n/iso‐selectivities between 0.7 and 2.6 have been observed. tert‐Butyl groups on the upper rim of the calix[4]arene template had a beneficial effect on the catalytic reaction. In general biuret‐derived P‐ligands were superior. For comparison, the corresponding “monomeric” ligands have also been synthesized and were employed in the catalytic reaction. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:577–585, 2001     

“Monte Carlo kinetics” for the simulation of photoreactions in polymers

We present a new method for describing photokinetics in the liquid crystalline or amorphous glassy state of polymers. A stochastic model has been developed in order to simulate the ordering process in azo side chain polymers which is induced by photoselective isomerization cycles. The dependence of the reorientation process on photochemical and thermal transition rate constants as well as the influence of matrix rigidity and cooperative interactions between the side chains is explained. With additional information about the molecular polarizabilities, the optical properties of the system, e.g. the evolution of birefringence, can be evaluated directly by this method.     

Investigation of the supramolecular structure of never dried bacterial cellulose

Supramolecular structure of initially wet bacterial cellulose of Acetobacter xylinum has been investigated by X-ray scattering including synchrotron radiation, transmission electron microscopy, and ¹³C-CP/MAS-NMR-spectroscopy. As a result a model is given of never dried swollen microfibrillar ribbons consisting of 5 to 12 waterfree I_α-crystalline subunits with a cross-section of about 7 nm × 13 nm and of water solvating the subunits. Lateral aggregation of these crystalline units was found along the smaller (110)-lattice planes with a layer of water between adjacent crystallites. The NMR-spectrum of wet bacterial cellulose exhibits an additional C-1 line component indicating cellulose-water interactions. During drying lateral dimensions of the microfibrillar ribbons, crystallite sizes, as well as the overall crystalline order decrease, whereas the Iα/Iβ-ratio of about 80/20 remains approximately unchanged. Conclusions were drawn with regard to the early states of structure formation of bacterial cellulose.