Total synthesis of the turrianes and evaluation of the DNA-cleaving properties

The first total synthesis of three naturally occurring cyclophane derivatives belonging to the turriane family of natural products is described. Their sterically hindered biaryl entity is formed by reaction of the Grignard reagent derived from aryl bromide 10 with the oxazoline derivative 18, and the macrocyclic tether of the targets is efficiently forged by ring closing metathesis. While conventional RCM catalyzed by the ruthenium-carbene complexes 33 or 34 invariably leads to the formation of mixtures of both stereoisomers with the undesirable (E)-alkene prevailing, ring closing alkyne metathesis (RCAM) followed by Lindlar reduction of the resulting cycloalkynes 37 and 38 opens a convenient and stereoselective entry into this class of compounds. RCAM can either be accomplished by using the tungsten alkylidyne complex [(tBuO)3 [triple bond] WCCMe3] or by means of a catalyst formed in situ from [Mo(CO)6] and para-trifluoromethylphenol. The latter method is significantly accelerated when carried out under microwave heating. Furthermore, the judicious choice of the protecting groups for the phenolic -OH functions turned out to be crucial. PMB-ethers were found to be compatible with the diverse reaction conditions en route to 3-5; their cleavage, however, had to be carried out under carefully optimized conditions to minimize competing O-C PMB migration. Turrianes 3-5 are shown to be potent DNA cleaving agents under oxidative conditions when administered in the presence of copper ions.     

Investigation of the fusion of heavy nearly symmetric systems

Excitation functions in the vicinity of the Coulomb barrier have been measured for the formation of evaporation residues in¹⁰⁰Mo-induced fusion reactions with^{90, 92, 96}Zr,^{92, 96, 98, 100}Mo,¹⁰⁴Ru and¹¹⁰Pd as well as for the system⁹⁶Zr+⁹⁶Zr. From these data the fusion probability in central collisions was extracted covering a range of 4 orders of magnitude. At the fusion barriers expected from systematics we find that the fusion probability is suppressed by one to three orders of magnitude. It is rising very gradually at higher energies and reaches for the heaviest systems saturation only at energies as high as 30 MeV above the barrier. The observed hindrance of the fusion process increases roughly with the growing Coulomb repulsion between the collision partners, but there is also a distinct influence of their individual nuclear structure. The data are compared to the extra-push model, the surface-friction model and the diabatic fusion model. A parameterisation of the extra-push energy and its fluctuation in terms of a macroscopic quantity like the Coulomb repulsion combined with a microscopic quantity characterizing the nuclear structure is proposed. As a byproduct of this work a new alpha emitter,¹⁹¹Po, could be identified. Its half-life is (15.5 _–2.5 ⁺⁶ ) ms, the alpha energy is (7314±20) keV.     

PH-Functional Methylenebisphosphanes RR′P-CH2-PRH (R′= R,H) - Reactive Bridging Ligands with A Small Bite Angle

Abstract

PH-functional methylenbisphosphanes RR′P-CH₂-PRH (R′=R, H) are versatile ligands in coordination chemistry. They may oxidatively add with their PH-bonds to transition metals in low oxidation numbers and form cluster compounds with P-C-P-bridges. P-C-P-bond cleavage reactions afford phosphinidenes ?PR?(through a formal 1,2-hydrogen shift from phosphorus to the CH₂-group, RR′P-CH₂-PRH → RR′P-CH₃ + ?PR?) which are incorporated into the oligometallic cluster framework formed.     

Fast calculation of HELAS amplitudes using graphics processing unit (GPU)

We use the graphics processing unit (GPU) for fast calculations of helicity amplitudes of physics processes. As our first attempt, we compute $u\overline{u}\rightarrow n\gamma$ (n=2 to 8) processes in pp collisions at $\sqrt{s}=14$  TeV by transferring the MadGraph generated HELAS amplitudes (FORTRAN) into newly developed HEGET (HELAS Evaluation with GPU Enhanced Technology) codes written in CUDA, a C-platform developed by NVIDIA for general purpose computing on the GPU. Compared with the usual CPU programs, we obtain a 40–150 times better performance on the GPU.     

Calculation of HELAS amplitudes for QCD processes using graphics processing unit (GPU)

We use a graphics processing unit (GPU) for fast calculations of helicity amplitudes of quark and gluon scattering processes in massless QCD. New HEGET (HELAS Evaluation with GPU Enhanced Technology) codes for gluon self-interactions are introduced, and a C++ program to convert the MadGraph generated FORTRAN codes into HEGET codes in CUDA (a C-platform for general purpose computing on GPU) is created. Because of the proliferation of the number of Feynman diagrams and the number of independent color amplitudes, the maximum number of final state jets we can evaluate on a GPU is limited to 4 for pure gluon processes (gg→4g), or 5 for processes with one or more quark lines such as $q\overline{q}\rightarrow 5g$ and qq→qq+3g. Compared with the usual CPU-based programs, we obtain 60–100 times better performance on the GPU, except for 5-jet production processes and the gg→4g processes for which the GPU gain over the CPU is about 20.     

ELEMENTS OF HIGH ORDER IN THE HOMOTOPY GROUPS OF HYPERBOLIC SPACES AT LARGE PRIMES

It is shown that rationally hyperbolic spaces do not admit ahomotopy exponent for their homotopy groups at almost all primes.