Metal-catalyzed chemoselective cycloisomerization of cis-2,4-dien-1-als to 3-cyclopentenones and 4-alkylidene-3,4-dihydro-2H-pyrans

[reaction: see text] PtCl(2) (5 mol %) catalyst effected cycloisomerization of cis-2,4-dien-1-al (1) to 3-cyclopentenone (3) efficiently in hot toluene. In the presence of p-TSA, this PtCl(2) catalysis gave 2-cyclopentenone (5) exclusively because of the secondary isomerization reaction. Although the 1-2 equilibrium state greatly favors aldehyde (1), PdCl(2)(PhCN)(2) (5 mol %) catalyzed cycloisomerization of aldehyde (1) to 4,6,7,8-tetrahydro-3H-isochromene (4) smoothly in hot toluene. A plausible mechanism is proposed on the basis of reaction observation and isotope-labeled experiment.     

Silsesquioxane-based nanocomposite dendrimers with photo-luminescent and charge transport properties

The synthesis and characterization of octavinylsilsesquioxane (OVS)-based nanocomposite dendrimers with luminescent and charge transport properties are reported. The nanocomposite dendrimers were prepared in high yield using mild Heck chemistry of mono-haloaromatic compounds with the peripheral vinylsilane groups of OVS. Attachment of 2-naphthalene, 2-(9,9-dimethyl)fluorene, and 2-(4-phenyl)-5-(1-naphthyl)-1,3,4-oxadiazole resulted in materials with blue-violet emission (360-380 nm) and photo-luminescent quantum efficiencies (PLQEs) from 1 to 26%. Blue-green emission was observed for attachment of 1-pyrene, 9-anthracene, and N1-(4-phenyl)-N1,N4,N4-triphenylbenzene-1,4-diamine with PLQEs ranging from 23 to 50%. Despite the planar characteristics of the organic dendrons, the nanocomposite dendrimers are completely amorphous and have high glass transition temperatures (Tg) ranging from 115 to 186 degrees C with decomposition temperatures (Td) exceeding 450 degrees C. Matrix-assisted laser desorption ionization-time of flight shows that unlike traditional Heck chemistry, haloaromatic compounds are adding twice across the vinylsilane groups. Finally, organic light emitting diodes using the aromatic amine-based dendrimer as hole injection layers show 55% improvement in device efficiency over traditional materials (5.16 vs. 3.24 cd A(-1)) with brightness levels exceeding 40,000 cd m(-2).     

Temperature tunable optical gratings in nematic elastomer

We have investigated the behaviour of temperature dependent periodic-index gratings fabricated in a nematic elastomer. The gratings have been obtained by photopolymerisation under a microscopy apparatus. Contraction properties, as well as diffraction properties, have been studied as a function of temperature. Unidirectional contraction has been demonstrated by means of circular figure deformation and the polarisation dependency of the diffraction by the gratings has been determined.     

Discovery of the shape coexisting 0+ state in 32 Mg by a two neutron transfer reaction

The "island of inversion" nucleus 32 Mg has been studied by a (t, p) two neutron transfer reaction in inverse kinematics at REX-ISOLDE. The shape coexistent excited 0+ state in 32 Mg has been identified by the characteristic angular distribution of the protons of the Δ L=0 transfer. The excitation energy of 1058 keV is much lower than predicted by any theoretical model. The low γ-ray intensity observed for the decay of this 0+ state indicates a lifetime of more than 10 ns. Deduced spectroscopic amplitudes are compared with occupation numbers from shell-model calculations.     

Synthesis of Activity Probes for β‐Xylosidase

Due to their industrial interest and significance, developing a rapid method for screening β‐xylosidase activities would certainly facilitate the research and improve production in xylan‐related industries especially in the pulp and paper industries. Here we report the synthesis of two activity probes, LCL‐ 6X and ‐ 12X , for β‐xylosidase. They both carry a β‐xylopyranosyl recognition head, which is linked to a latent trapping device consisting of a 2‐fluoromethylphenoxyl group and a biotin reporter group. They differ only in the length of their hydrophobic linker. A model study using a β‐xylosidase from T. koningii demonstrates that both probes could successfully label the target hydrolase and give rise to biotinylated proteins. They could thus potentially become a powerful tool in screening β‐xylosidase from microbial sources.     

Collisions of complexes of weakly coupled laser solitons

Different scenarios of collisions of complexes of weakly coupled solitons moving in antiparallel directions in a wide-aperture class-A laser with saturable absorption are found by numerical simulation. Depending on the impact parameter and the phase difference of the initial complexes, they can adhere to each other or form new complexes composed of both initial complexes, while the number of solitons can change from their total disappearance to the extension of the region of generation over the whole transverse cross section of the laser.     

Halocyclization of Methyl 2‐Alkynylbenzoates to Isocoumarins Using Cupric Halides

Treatment of methyl 2‐alkynylbenzoates with two to three equivalents of CuX₂ (X = Cl or Br) in refluxing acetonitrile gave isocoumarins 2 in good to excellent chemical yields.     

A dynamical model of electoral competition

The paper presents the specific framework and a set of simulations computed on the basis of a kinetic model of interest in the field of the Social Sciences. The model is a reduced version of a comprehensive more general one, and it relates to the specific case of a competing bipartisan political system. The model structure contains terms with localized interactions and mean field terms. In the first part of the paper the mathematical details of the model are recalled. In the second part the simulations are presented with reference to the various scenarios examined. Finally a discussion on research perspectives is formulated.