Cocyclotrimerization of 6-alkynylpurines with alpha,omega-diynes as a novel approach to biologically active 6-arylpurines

Transition metal complex catalyzed cocyclotrimerization of 6-alkynylpurines 1 with various diynes enables the preparation of a plethora of substituted 6-arylpurines 3 in good yields. The most general catalyst for the reaction is a user-friendly system based on a nickel-phosphine complex and reductant (NiBr(2)(dppe)/Zn) in MeCN. The reaction conditions are compatible with various protective groups on the purine moiety (Bn, THP). As far as other potential catalysts were concerned, only CoBr(PPh(3))(3) showed reasonable activity in cocyclotrimerization of alkynylpurines with dipropargyl ether. A comparison of catalytic with stoichiometric approaches and the ligand effect in the catalyst is also given. Cytostatic activity screening of title 6-arylpurines was performed and several moderately active compounds were found.     

Intramolecular exchange interaction in twofold spin-labelled platinum complexes

The synthesis and the crystal structures of two platinum bis-ethynyl-phenyl-nitronyl-nitroxide complexes are reported and solution EPR investigations evidenced the intramolecular exchange interaction through a diamagnetic transition metal based spacer.     

A TEST OF CLOSE-RANGE PHOTOGRAMMETRY

Care was taken to generate high-contrast targets for calibration and measurements. These target coordinates were documented with an order of magnitude more accuracy than achievable using photogrammetry. The repeatability of the film measurements was also an order of magnitude more accurate than photogrammetric coordinate determinations.
The best accuracy for in-plane measurements of X or V was approximately 0.2 percent (1 part in 500) and 0.4 percent (1 part in 250) for range Z measurements.
It is not obvious how the accuracy can be easily increased using this hardware; measurements for the purpose of quality control of typical parts manufactured by machining and grinding is out of the question.
Measurements for quality control of bent sheet metal may be possible. Certainly automobile accident reconstruction scenes, general archiving, and similarly relaxed environments have applications for this accuracy.
This fine-grain film with its 35-mm format has an order of magnitude more resolution than a typical solid state CCD imager. Furthermore, it is difficult to perceive object targets which result from features of the part itself that would even approach the contrast of the special targets used here.
More accuracy is, however, obtainable from convergent cameras, redundant cameras, calibrated optics/principal points, large-film format, stereo-plotter measurements, and error minimization techniques.     

Proton-hole states in 57Co studied with the 58Ni(d, 3He) 57Co reaction at 78 MeV

The ⁵⁸Ni(d, ³He)⁵⁷Co reaction was measured at a bombarding energy of 78 MeV. Energy levels up to 7.0 MeV excitation energy in ⁵⁷Co were studied. Angular distributions of the ³He particles, corresponding to transitions to the ground state and to 42 excited states in ⁵⁷Co, were analyzed in the range of θ_lab = 2.7° to 25°. Exact finite-range DWBA calculations were employed to extract l-values and spectroscopic factors. Shell-model calculations were carried out in an fp-shell model space. In addition, calculations of the energy levels in ⁵⁷Co were performed in the SU(6) particle-vibration model (PTQM). Satisfactory agreement is observed between the experimental results and both theoretical predictions.     

Ab-initio theory of the CPP-magnetoconductance

The current-perpendicular-to-plane (CPP) magnetoconductance of a trilayer consisting of a spacer sandwiched between two ideal leads is described on anab initio level. We employ the transmission matrix formulation of the conductance within the framework of the spin-polarized surface Green function technique as formulated in terms of the tight-binding linear muffin-tin orbital method. The formalism is extended to the case of lateral supercells in each layer with random arrangements of atoms which allows to treat both the ballistic and diffusive transports on equal footing. The application is made to fcc-based Co/Cu/Co(001) trilayers. Presented at the VIII-th Symposium on Surface Physics, Třešt’ Castle, Czech Republic, June 28 – July 2, 1999. Financial support for this work was provided by the Grant Agency of the Czech Republic (Project No. 202/97/0598), the Grant Agency of the Academy of Sciences of the Czech Republic (Project A1010829), the Center for the Computational Materials Science in Vienna (GZ 45.442 and GZ 45.420), the Austrian BMWV (AKTION WTZ-?sterreich-Tschechien I.23), MŠMT ČR (Project COST P3.70), and the TMR Network ‘Interface Magnetism’ of the European Commission (Contract No. EMRX-CT96-0089).     

Organogermanium(II) Hydrides as a Source of Highly Soluble LiH

The reactions of monomeric C,N-chelated organogermanium(II) hydride L(H)Ge ⋅ BH₃ with organolithium salts RLi yielded lithium hydrogermanatoborates (Li(THF)₂{BH₃[L(H)GeR]})₂. Compound (Li(THF)₂{BH₃[L(H)GePh]})₂ was used as a source of LiH for the reduction of organic C=O or C=N bonds in nonpolar solvents accompanied by the elimination of a neutral complex L(Ph)Ge ⋅ BH₃. The interaction of (Li(THF)₂{BH₃[L(H)GePh]})₂ with the polar C=O bond was further investigated by computational studies revealing a plausible geometry of a pre-reactive intermediate. The experimental and theoretical studies suggest that, although the Li atom of (Li(THF)₂{BH₃[L(H)GePh]})₂ coordinates the C=O bond, the GeH fragment is the active species in the reduction reaction. Finally, benzaldehyde was reduced by a mixture of L(H)Ge ⋅ BH₃ with PhLi in nonpolar solvents.     

Do Spectra Live in the Matrix? A Brief Tutorial on Applications of Factor Analysis to Resolving Spectral Datasets of Mixtures

Journal of Fluorescence - In spite of a rapid growth of data processing software, that has allowed for a huge advancement in many fields of chemistry, some research issues still remain problematic....     

Influence of higher interpolation orders in mixed LSFEM for the incompressible Navier-Stokes equations

The focus of this contribution is the examination of the influence of different interpolation orders (especially for the pressure field) by solving the stationary incompressible Navier-Stokes equations with least-squares finite elements. We consider two different div-grad first-order systems which result in a three-field formulation with stresses, velocitites and pressure, see e.g. SCHWARZ & SCHRÖDER [1] and BOCHEV & GUNZBURGER [2]. Additionally, a numerical example is presented to show the performance of the considered formulations. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)