Synthesis of nucleoside dimers bridged on ribose with a butadiynyl group

[reaction: see text] The nucleoside dimer linked by a butadiynediyl group at C-3'beta may serve as a building block for the preparation of backbone-modified oligonucleotides for DNA repair or mutation in functional genomics. We prepared this type of dimer by an Eglington or Sonogashira coupling reaction. The unsymmetrical dimer was synthesized by coupling the acetylene with the bromoacetylene. Only marginal cytotoxicity was detected for one of the dimers.     

Une remarque sur l’inégalité de McKean

Résumé Pour une classe de variétés riemanniennes équipées de métriques tordues, nous donnons dans ce travail une borne inférieure optimale pour la première valeur propre du laplacien dans le problème de Dirichlet. Linégalité présentée, qui est obtenue très simplement, étend celle de McKean à des variétés dont la courbure peut être de signe variable. Cest le principal intérêt de linégalité. Elle répond aussi partiellement à une question de Schoen et Yau.      

Rational improvement of centrifugal partition chromatographic settings for the production of 5-n-alkylresorcinols from wheat bran lipid extract. I. Flooding conditions--optimizing the injection step

A dedicated CPC prototype permits direct flow pattern visualization in the partition cells of a CPC column. It was used to understand "flooding", a frequent phenomenon associated with large injections. A general strategy was developed to optimize the injection step in the framework of a particular preparative separation: the purification of 5-n-alkylresorcinols from a wheat bran lipid extract on a several hundred milligram scale. The construction of the "mobile phase/stationary phase/sample" pseudo ternary diagram characterizes the effect of the injected solution on mobile and stationary phases. The position of the binodal curve maximum indicates if the biphasic system is "robust" towards a large injection or not, and can be used for optimum mass load determination.     

On the Rate of Convergence of Two Bernstein–Bézier Type Operators for Bounded Variation Functions

In this paper we study the rate of convergence of two Bernstein–Bézier type operatorsB^(α)_nandL^(α)_nfor bounded variation functions. By means of construction of suitable functions and the method of Bojanic and Vuillemier (J. Approx. Theory31(1981), 67–79), using some results of probability theory, we obtain asymptotically optimal estimations ofB^(α)_nandL^(α)_nfor bounded variation functions at points of continuity and points of discontinuity.     

Variational method for calculating molecular multipole polarizabilities using atom centered extended trial functions

An improvement of the variational method for calculating the electronic multipole polarizabilities is proposed. This modification allows the computation of the polarizabilities at any point and the results are compatible with the relations existing for a change of origin. It is applied to H₂, HF, CO and N₂ by using SCF wavefunctions developed on a limited basis. The computed polarizabilities are systematically too large but this discrepancy is attributed to the fact that the ground state is too far from the exact wavefunction.E.R.A. au C.N.R.S. No. 22.     

End-on versus side-on coordination of dioxygen model ab initio calculations for the adducts of Co(acacen)

From ab initio calculations, the ground state electronic configuration is found for the three possible structures (linear, bent or perpendicular) of the cobalt-dioxygen unit in the adducts Co(acacen) LO₂(L=none, H₂O, CN^?, CO). The bent structure is energetically the most favourable, being slightly more stable than the linear one (by 4–26 kcal/mole depending on the fifth ligand L) but much more stable than the perpendicular one (by 46–82 kcal/mole). These results are rationalized in terms of the main metal-ligand interactions, with the bent structure stabilized by a 3d _z ²-1π _g ^/a interaction and the perpendicular structure destabilized by a four-electron destabilizing interaction 3d _xz -1π _g ^/a .     

Polymerization of hex-1-ene initiated by diimine complexes of nickel and palladium

The effect of monomer concentration, reaction temperature and initiator structure on the activity, molar mass, branching and thermal properties of poly(hex-1-ene)s was investigated for the polymerization of hex-1-ene initiated by four α-diimine complexes of nickel and palladium. Hex-1-ene polymerization exhibits an apparent negative kinetic order with respect to monomer concentration. Polymerization of hex-1-ene initiated by MAO activated 1,4-bis(2,6-diisopropylphenyl)acenaphtenediiminenickel(II) dibromide (1a/MAO) proceeds in living-like fashion not only at sub-zero temperatures but even at 20 °C. However, molar masses of the polymers are higher than predicted values in agreement with an initiator efficiency lower than one.     

Synthesis,structure and reactivity of imidazo[1,2-a][1,8]naphthyridines

The synthesis and reactivity of imidazo[1,2-a][1,8]naphthyridines are reported. Electrophilic substitution reactions were studied and the site of the reaction was established with the aid of high-field ¹H and ¹³C nmr spectra. The experimental C-1 position reaction was correlated with a CNDO/2 calculations.     

CLIP: similarity searching of 3D databases using clique detection

This paper describes a program for 3D similarity searching, called CLIP (for Candidate Ligand Identification Program), that uses the Bron-Kerbosch clique detection algorithm to find those structures in a file that have large structures in common with a target structure. Structures are characterized by the geometric arrangement of pharmacophore points and the similarity between two structures calculated using modifications of the Simpson and Tanimoto association coefficients. This modification takes into account the fact that a distance tolerance is required to ensure that pairs of interatomic distances can be regarded as equivalent during the clique-construction stage of the matching algorithm. Experiments with HIV assay data demonstrate the effectiveness and the efficiency of this approach to virtual screening.