Site-selective direct arylation of unprotected adenine nucleosides mediated by palladium and copper: insights into the reaction mechanism

Reaction conditions facilitating the site-selective direct aryl functionalisation at the C-8 position of adenine nucleosides have been identified. Many different aromatic components may be effectively cross-coupled to provide a diverse array of arylated adenine nucleoside products without the need for ribose or adenine protecting groups. The optimal palladium catalyst loading lies between 0.5 and 5 mol %. Addition of excess mercury to the reaction had a negligible affect on catalysis, suggesting the involvement of a homogeneous catalytic species. A study by transmission electron microscopy (TEM) shows that metal containing nanoparticles, ca. 3 nm with good uniformity, are formed during the latter stages of the reaction. Stabilised PVP palladium colloids (PVP=N-polyvinylpyrrolidone) are catalytically active in the direct arylation process, releasing homogenous palladium into solution. The effect of various substituted 2-pyridine ligand additives has been investigated. A mechanism for the site-selective arylation of adenosine is proposed.     

Vortex dynamics in the wake of a mechanical fish

A novel Stereo PIV technique, with improvements over other techniques, is presented. The key feature of the new technique is the direct measurement of calibration data at each point in space on the measurement grid, so that no interpolation is necessary. This is achieved through the use of a contiguous target which can be analysed using standard PIV processing software. The technique results in three-dimensional measurements of high accuracy with a significantly simpler calibration phase. This has the benefit of improving ease of use and reducing the time taken to obtain data. Thorough error analysis shows that while previously-described error trends are correct, additional facets of the technique can be optimised to allow highly accurate results. The new technique is rigorously validated here using pure translation and rotation test cases. Finally, the technique is used to measure a complex swirling flow within a cylindrical vessel.     

Physical preseparation for chemistry experiments

The availability of physically preseparated isotopes for chemistry experiment opens up completely new possibilities, especially for chemical investigations of transactinide elements. Many restrictions present in conventional methods that were used very successfully in the past can be overcome by using preseparated isotopes. An overview of experiments that were performed with preseparated isotopes is given. Studies of β-diketonates of group 4 elements are described in some more detail and used as an example to demonstrate the power of the method. Production of preseparated long-lived transactinide isotopes is outlined and, lastly, the new preseparator TASCA which is currently being installed at GSI, Darmstadt, is briefly described.